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  #1  
Old 02-27-2010, 4:43 AM
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Default Heckler & Koch G3 Build

Heckler & Koch G3 Build

Fixing/Building/Putting together your own guns can/may cause serious harm, up-to and including death! That is a good reason why professional/qualified gunsmiths exist, make use of them. Do know your laws, many that may apply to you may not be mentioned here. Some images used here for illustration (with permission from the rightful owner) are NFA regulated items under current laws, they require special permits and licensing and may be completely prohibited in your State. This thread of mine is for pure educational purposes. It is not my intention in any way to get you to follow.

All images used from the Wikipedia and Photobucket are used under their Proprietary Rights in Content policy . Images that are proprietary are being used by first obtaining written Permission from the rightful owner. This material may not be copied, edited, reproduced or distributed without prior permission from the original owner. By mentioning any commercial vendors or by using their material does not benefit me in anyways.

Prerequisite: For people familiar with the HK family. Armorer level knowledge is not covered here i.e. stripping a Bolt-Head, or disassembling a Trigger Pack. You will need good mechanical skills, tools and pertaining knowledge i.e. we will not be covering how to weld. I have no experience with a CETME, below thread may or may not apply to them.


There are many other documented HK builds (semi-complete in most cases) on various boards, at the very end I will post some links to them. If you wish to get into further/deeper detail you can search archives on HKPro forum or Special Topics



Principal behind building a 91 (G3), 93 (HK33), 94 (HK MP-5) or the SP-89 (PDW) TYPE OF SEMI AUTO GUN is basically the same. If you can do one, you can do the others or anything in between with a little chopping and welding, i.e. the 51 or 53. Even guns like PSG-1, MSG-90, H&K 11, H&K 21 and H&K 23 can be built (if you can find parts). Although I am building a (Calif. Legal) Semi-Auto G3 copy, I will be making small reference to the 5.56 and the 9mm guns.


Last edited by fredieusa; 03-12-2010 at 9:06 PM..
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Old 02-28-2010, 11:29 PM
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For ease of reference and clarity I am numbering headers thought this build. They can be further branched out to the very last washer and screw but is not necessary. Here is the Road Map. Most of the pictures are AFTER the description and run left to right, top to bottom. I can only post limited number of pics in each post, so bear with me.

1.0.0.0 Kit
-1.1.0.0 Front End
-1.2.0.0 Trigger Group
-1.3.0.0 Butt Stock Assembly
-1.4.0.0 Small Parts
-1.5.0.0 Other Parts needed – Essential.
-1.6.0.0 Other Parts needed - Optional.
-1.7.0.0 922(r) Parts Count and List of Suppliers


2.0.0.0 Preparing the Kit and Parts
-2.1.0.0 Checking Head-Space
-2.2.0.0 Marking Front Sight Post and Bolt Guide Tube / Cocking Tube
-2.3.0.0 Demilling the Trunion from the receiver stub
-2.4.0.0 Demilling the Bolt Guide Tube / Cocking Tube
-2.5.0.0 Salvaging Rear Sight Base (RSB)
-2.6.0.0 Salvaging Reinforcement Plate for rear push-pins (and stock pin sleeves)
-2.7.0.0 Salvaging Paddle Mag Release


3.0.0.0 Parts Conversion to Semi-Auto
-3.1.0.0 Eliminating Select Fire parts.
-3.2.0.0 Trigger pack housing / body cutting and welding.
-3.3.0.0 New pin location for Sear Spring.
--3.3.1.0 Bending of the Spring.
-3.4.0.0 Internal Trigger Stop Pin.
--3.4.1.0 New Pin location.
--3.4.2.0 Drilling for the new pin.
--3.4.3.0 Installing the new Stop Pin and securing with a weld.
-3.5.0.0 Hammer Work
-3.6.0.0 Trigger Work
-3.7.0.0 Converting the Trigger pack housing / Clipping and Pinning.
--3.7.1.0 Making a Semi-Auto Shelf
--3.7.2.0 Fitting the Semi-Auto Shelf.
--3.7.3.0 Welding the Semi-Auto Shelf.
--3.7.4.0 Clipping off the ears / Cutting off the tabs – Grinding the Tabs.
--3.7.5.0 Installing Push-Pin bits
-3.8.0.0 Bolt Carrier


4.0.0.0 Receiver Building and Completion
---4.0.0.1 Complete Receivers
---4.0.0.2 Flats
-4.1.0.0 Bending the Flat.
--4.1.1.0 Squaring the rails
--4.1.2.0 Forming / bending the flat
-4.2.0.0 Welding the Receiver
--4.2.1.0 Conforming the receiver to specification.
---4.2.1.1 Receiver Rails
---4.2.1.2 Lower Opening
---4.2.1.3 Trigger Housing fit
---4.2.1.4 Magazine Well
---4.2.1.5 Stock / Back Plate Mounting
--4.2.2.0 Magazine Catch
--4.2.3.0 Welding the Semi-Auto Wedge (Shelf).
--4.2.4.0 Welding rear Push-Pin support and sleeves.
-4.3.0.0 Welding / Installing the Trunion (barrel), Charging Tube and Rear Sight
---4.3.0.1 Preparing the Trunion
---4.3.0.2 Preparing Charging Tube
---4.3.0.3 Preparing Rear Sight
---4.3.0.4 Setting up the Boresighter
--4.3.1.0 Drilling Barrel Retaining Pin Holes and Chamfer Receiver Edge
--4.3.2.0 Mocking-up Trunion and Charging Tube in Receiver
---4.3.2.1 Boresighting
---4.3.2.2 Fixing Canted/Misaligned Barrels
---4.3.2.3 Trunion and the Rails
---4.3.2.4 Rear Sight
--4.3.3.0 Welding the Rear Sight Base
--4.3.4.0 Welding Trunion
---4.3.4.1 Drilling Holes for Barrel Retaining Pin
--4.3.5.0 Welding Charging Tube


5.0.0.0 Installing a paddle magazine release

6.0.0.0 Issues.

-6.1.0.0 Bolt Carrier
-6.2.0.0 Rails and Trunion
-6.3.0.0 Hand Guard Fit
--6.3.1.0 Correcting Charging Tube location


7.0.0.0 Refinishing of Metal

8.0.0.0 Refinishing of Wood

9.0.0.0 Range Report and Notes

Last edited by fredieusa; 03-07-2010 at 2:04 PM..
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Old 02-28-2010, 11:29 PM
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1.0.0.0 The Kit

All kits are well built. Depending on the origin, basic accessories included and the condition, you can expect to pay anywhere from $300-$700. Other factory accessories like the scope mounts ($250 - $650) are most likely going to be extra. Receivers and other materials required for building are also extra.

Parts can be readily interchanged between all the G3 variants. Unlike the German WW2 stuff, or even builds such as AK from demilled kits, the serial number is not stamped all over the place, this alone saves some headache.

Your kit should have four basic identifiable parts. Front end, trigger group, butt stock assembly and small parts bag.



Notes on Furniture: Furniture usually refers to the Hand-Guard, Pistol Grip and Butt Stock. All furniture is interchangeable if you have an original type sheet metal receiver. Cast Aluminum receivers use the older slim Hand-Guard, wide can be used after heavy modifications. Usually all three items should match in color, but is you use the wood Hand-Guard and Butt-Stock, a black pistol grip goes just fine.



These Schematics http://www.robertrtg.com/g3schematic.html may help in identifying parts. Make note that these schematics are of a G3 Rifle, your parts should match.



These schematics are from a H&K 91 Semi Auto Rifle. Visible difference is in the receiver (behind the mag well) and the Fire Control parts with their housing.


Last edited by fredieusa; 03-12-2010 at 9:03 PM..
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Old 02-28-2010, 11:30 PM
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1.1.0.0 Front End



Muzzle Device

Barrel: It is pressed into the Trunion and is retained there by a cross pin.

Front Sight Post a.k.a Tripple Tee: A dust cover made of Aluminum or Steel goes in the middle. It has a spring loaded indent that is used to secure the cover to the Post. The indent locks into a hole when pushed into the Post

Trunion

Hand-Guard (Forearm): The older styles are narrow (slim) as pictured kit above. They were made of wood or plastic (black and green). The Newer Style usually refers to the wide forearm made of plastic. They usually come in Black, Green and even Beige (Earth). All wide Hand-Guards have a slot for bi-pod mount at the front end, and a leaf spring lock for the bi-pod on the underside. Most quality wide forearms also have a hook on rear left side meant for use with three point sling. Cheaper ones do not have the heat shield liner inside.





Bolt Guide Tube / Cocking Tube: Bolt carrier rides in this. Although the carrier does not travel all the way till the Front Sight Post, it does travel to almost the charging handle resting position.

Dents deep enough on the tube will obstruct the action by blocking the free movement of the carrier, and cause malfunction. You can fix the dents easily or get a replacement. They are easily available.



Bolt Carrie Group complete.

Bolt Carrier, Bolt Head, Locking Piece, Firing Pin and Spring: Bear in mind that not all locking piece are the same. They bear identifying numbers and vary at the angle at which they taper.

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Old 02-28-2010, 11:30 PM
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1.2.0.0 Trigger Group





Grip Frame and selector.

Sear Pack - Skeleton Box Housing, Hammer, Hammer Shank, Spring and Pivoting Pin. Sear Catch, Sear Spring (Elbow Spring), and Trip Lever, Spacer, Roller and Pivoting Pin. Trigger, Sear, Trigger Spring and Pivot Pin.




Pistol Grip: All are made up of plastic and come in three colors, Black, Green and Beige (Earth).
They are secured to the metal Trigger Housing Frame with a lock washer and a screw.



The newer Trigger Housing Frame is a single unit, molded in plastic as one piece incorporating the Pistol Grip. They come in black and are lighter in weight than the older version.

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Old 02-28-2010, 11:31 PM
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1.3.0.0 Butt Stock Assembly

Fixed stock is made of wood or plastic. The plastic come in the same three colors, Black, Green and Beige (Earth). Some after-market plastic ones do not have the sling loop anchor slot or the holes for back plate (butt plate cover) retainer. There are a lot of styles available now, including telescopic (M4 type) ones.



Collapsible or Telescopic. These are very sold and have a lesser known older style. The older style was all metal and had a slight contour along the shoulder. The newer style has a rubber cushion attached and is bowed at the end.



Side Folding. Not as popular, I have no personal experience with this. BTW Choate is an OEM.



Buffer
Recoil Guide Rod and Spring


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Old 02-28-2010, 11:31 PM
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1.4.0.0 Small Parts

The kit will have a small parts bag. You will need to sort them into two as following.

Rear Sight Parts – rear sight Main Block with Elevation Rotating Drum, oval washer, lock washer, attaching screw, detent ball, detent ball spring, windage adjustment screw.



Magazine Catch, Magazine Catch Arm, Paddle Flap Release (two kinds), Lock (Contact Piece), Sleeve, Push Button and Cotter Pin

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Old 02-28-2010, 11:32 PM
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1.5.0.0 Other Parts needed – Essential.

These parts are a MUST. If you did not get them with your kit, you will need to buy them or make your own.

Receiver / Flat

Here you have two choices. You can buy a complete receiver and skip right over to demilling in the next section or get yourself a flat, which will need to be formed, welded, and parts attached /welded to it.

Complete PTR Receiver: These PTR receivers are a piece of art! The closest thing I have seen to the original. Down to the very last detail that matters. Semi shelf installed. Rear sight base installed. Rails are square. Stampings are nice and sharp, and most importantly it has the rear receiver reinforced that houses the two bushings. I highly recommend it.

Sorry, did not have time to e-mail PTR to get permission for using their photo.

PTR http://www.hkparts.net/shop/pc/viewP...?idproduct=772

Flat: The one I have was probably bought from Copes. They are widely available at various places now.

On MilitaryFirearms, Blackwing selld flats with some updates! You will have to read the complete thread to know what he offers.
Here is the link.



Shelf for Semi-Auto Receiver. This part, when welded to the rear of the magazine well, prevents the Select Fire Trigger housing from attaching.

Rear Sight Base. You can either buy a new one or extract one from a demilled receiver.

http://www.robertrtg.com/receiverflat.html


Last edited by fredieusa; 03-06-2010 at 9:25 PM..
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Old 02-28-2010, 11:32 PM
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1.6.0.0 Other Parts needed - Optional. These are not essential to complete a functioning rifle, but they may save you time and effort. Also I am including some items (or description of) which I find are important to reinforce the structural integrity, just like the original HK.

Sear Pack already converted to Semi Auto. For whatever reason if you choose not to convert your own.



Trigger Housing already Clipped, Pinned and shelf welded.
For whatever reason you wish not to convert your own as explained in section 3.0.0.0-Parts Conversion to Semi-Auto



Shelf for Semi Auto Trigger Housing.
Looks similar to the Shelf for the receiver, But not the same thing.

Bushings (2) for rear butt stock push pins.
Maybe not commonly used, but I highly recommend it.

Reinforcing Shelf for rear receiver push pin bushings
This sheet metal piece is welded (and spot welded on the sides) to the receiver, then bushings are inserted and welded. Installing this reinforces the lower rear of the receiver and makes it rigid and strong. All factory guns have this installed.

I am reclaiming this from a demilled receiver stub as shown in section 2.6.0.0. Because it is a demilled item, instillation will be different. (Shown in the middle below).

Blackwing on MilitaryFirearms.com offers these also. Here.

Paddle Magazine release
I will be installing a Paddle Mag-Release, Here is a very desirable upgrade. The anti rattle lever, it improves magazine fit (feeling) and rattle.
http://www.hkparts.net/shop/pc/viewP...6&idcategory=0



Bushings for sear spring

These bushings / washers will fill in the gap created by the elimination of the sear catch (full auto part).

PIC needed

Last edited by fredieusa; 03-06-2010 at 9:11 PM..
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Old 02-28-2010, 11:33 PM
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1.7.0.0 922(r) Parts Count and List of Suppliers http://www.922r.com/

I am building a rifle here, so 922(r) applies. If it were a pistol build, it would not have applied.
HK91 type build involves 17 parts, that means I am required to use at least 7 US Made parts (10 foreign parts are allowed). As you can see below, I have plenty of choices (ones listed in color Purple ) of domestically made parts to choose from.


1 Receiver
2 Barrel
3 Trunion
4 Muzzle Attachment
5 Bolt
6 Bolt Carrier
7 Operating Rod
8 Trigger Housing
9 Trigger
10 Hammer
11 Sear
12 Butt Stock
13 Pistol Grip
14 Hand Guard / Forearm

* There are Thermold G3 mags available. They count as 3 US made pats*

15 Magazine Body
16 Magazine Follower
17 Magazine Floor Plate


Here is a partial list of vendors that offer parts [also 922(r) compliant US Made-parts]. Although I have not dealt with all on the list, most are upstanding. In addition to the list below, you can also try auction sites, various boards and classifieds like http://www.hkpro.com and http://www.sturmgewehr.com

http://www.robertrtg.com/
http://www.hkparts.net/shop/pc/home.asp
http://www.copesdistributing.net/index.php?cPath=32_41
http://www.centerfiresystems.com/g3.aspx
http://www.hkspecialiststore.com/index.php
http://www.rimcountrymfg.com/guns.htm#guns
http://www.shop.black-market-parts.com
http://www.ptr91.com/store/cart.php
http://www.top-notchparts.com/parts_for_91_93_94.htm
http://store.bravo5.com/servlet/-str...-HK/Categories
http://www.gunpartscorp.com/catalog/...spx?catid=8932
http://www.lscmanufacturing.com/products.php
https://www.apexgunparts.com/index.php/cPath/42
http://scorpion-arms.com/cart.php

$29 only flats !!

http://rapidfire.targetweb.net/cgi-b...m=on&ppinc=big

Last edited by fredieusa; 03-07-2010 at 5:29 PM..
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Old 02-28-2010, 11:33 PM
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2.0.0.0 Preparing the Kit and Parts

As we disassemble and demill the kit, keep an eye out for excessively worn parts that may be critical to the safety and functioning of your gun.

2.1.0.0 Checking Head-Space .3 to .4

We check headspace now. The HK delayed Roller lock action do not require a Head-Spacing Gauge, instead we will use a feeler Gauge. Factory sets head space between 0.3mm and 0.4mm. Safe working limit is between .2mm and .5mm. If I can get a gauge in there between .2mm and .5mm it will be safe. If it is between .3mm and .4mm, that will be ideal.

To check the headspace I lock the bolt carrier group into the Trunion. It needs to seat all the way and lock-up. The head space is measured by gauging / measuring the space between the carrier and the bolt head.

In the extend position the bolt group is unlocked. When the bolt head is seated all the way, it is locked. Now we insert our feeler gauge and check headspace. This one here comes in at .203mm / .008”. Almost on the line towards the lower limit, but I will live with this. Depending on how much I shoot it, it may become necessary to visit this again. More the gun/parts wear out, less the head-space gets.





Correcting Head Space

Using a different size of Rollers or replacing your Locking Piece will correct your Head-Space.
Here is what rollers come in. You determine if you your have less or excessive head space, then choose your parts accordingly. If you increase your roller size by +2, your Head-Space (Gap) will increase by .02mm. here are some threads on the subject.

http://hkpro.com/forum/showpost.php?...63&postcount=5
http://www.hkpro.com/index.php?optio...opics&Itemid=5
http://www.hkpro.com/index.php?optio...layout=default


Last edited by fredieusa; 03-14-2010 at 8:43 PM..
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Old 02-28-2010, 11:33 PM
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2.2.0.0 Marking Front Sight Post and Bolt Guide Tube / Cocking Tube

Before I start cutting metal and moving things around, I mark the depth and angle relationship between the tube and the front sight post. This step simplifies the task of installing the Tube back again.

I place a tape on the tube that touches flush with the Front Sight Post, this marks my depth. For indexing (angle) I draw a straight line across the Front sight post and over the tape. Once it is time to weld the tube to the new receiver, matching up the location will be a breeze.



You may also directly scribe them using a sharp object.

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Old 02-28-2010, 11:33 PM
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2.3.0.0 Demill the Trunion from the receiver stub

Locate spot welds on your receiver stub, over Trunion area. There should be a total of four, one on each side and two at the bottom. These spot welds are what bind the receiver to the Trunion.



In order to separate the Trunion from the receiver stub, we will need to eliminate these spot welds. You may use any method to accomplish this, as long as you do not drill into the Trunion. I prefer to start with an end-mill, anything around 9/16th or 7mm will be ideal.

While securing your front end in the vice, you need to be careful as to not dent or marr the Bolt Guide Tube / Cocking Tube. As you are working on a curved surface, end mills will cut on a level. This leaves a potential for the end mill to eat into the Trunion even before the weld completely pops. I do not mill all the way as I don’t wish to risk drilling into the Trunion.



With most of the spot weld milled, now use a hack saw or a dremel to cut along the bottom of the receiver and through the magazine well. Once the cut is complete, use a chisel to open up the gap and start to peel away. As you peel the receiver away, any material still holding the spot welds will pop.

Damaging the Bolt Guide Tube / Cocking Tube in this process is common because you will be swinging hammers and chisels to peel off the receiver stub off the Trunion, while the Tube is still connected. Saving the tube is not hard, just remain aware where the tube is when working.



Secure one of the ears of the mag well into a vice, that will hold it in place while you hammer away using a chisel. The receiver is also welded to the Trunion at the rails, they give fairly easy. Continue to pop the last two spot welds on the Trunion till it is free. Now that we have the Barrel (barrel, Trunion & FSB) and Bolt Guide Tube / Cocking Tube separate, store the barrel away as it will not be needed till the receiver is complete and ready in Section 4.3.0.0

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Old 02-28-2010, 11:34 PM
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2.4.0.0 Demilling the Bolt Guide Tube / Cocking Tube

Should your Tube get damaged or dented where you are unable to fix, there are replacements available. You can also buy new ones, which will save you time and effort, nothing beats that. Your kit is expensive, so is everything H&K. Don’t wait for a visual disappointment in the end trying to save a few bucks. Here is ours, no dings or dents fortunately. I worked very carefully to make sure of that. Notice I still have my tape up front.



Next I take off the receiver stub from the tube while retaining the (whole) extension. This original extension has a beautiful bevel job, moreover the bolt in normal battery does not travel far enough (rearwards) to clear the extension. Should these measurements be decreased, the bolt carrier will have a rougher ride.

Start with milling out or grind off two spot welds, one on each side. Mill most of the way and peel the rest off, just like the Trunion. I will also place a shallow cut along the border of the tube and the receiver. The cut is placed just behind the weld away from the tube. Once the cuts are made, again (just like the trunion) I will tightly secure one of the receiver’s mag well ears in a vice and try peeling it off. The tube extension is thin, so I have to be careful as to not squash it.



The complete extension is recovered. Use a Dremel and square-out the extension at the base.

As you can see I did not mill enough, which left the receiver material stronger than the extension causing holes in the extension .. Oops! The holes that were caused due to peeling were later repaired.



THERE IS AN ALTERNATE METHOD. Cut off the excess receiver portion that enveloped the Trunion. Leave the receiver stub around the extension tube. Using a belt sander, eliminate the receiver stub. This saves you the milling for the spot welds and no peeling off. I don’t use this method because I find hard to achieve uniformity while belt-sanding around a cylindrical object.
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Old 02-28-2010, 11:34 PM
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2.5.0.0 Salvaging Rear Sight Base (RSB)

Most folks buy a new one. You can reclaim one if you have a receiver rear end (or buy the demilled section from RobertRTG). Use a Dremel and cut through the receiver along the edges of the Sight Base.



Once the RSB is free, grind off the receiver stub on the rear and match it to the rear of the RSB. Then start grinding at the lower edges. When you start to come close to .26”, the RSB will start to separate from the receiver stub attached to it because you have ground off the weld.



Cut towards the front end on both sides straight down, this frees up any welds on the sides. For the front end, you can see where the metal is welded on the underside. Use a Dremel to clean the area around the weld cutting into the receiver. While doing this, do not cut into the Sight Base. Give a few light taps with a punch and the receiver stub will comes loose. Dress up the recovered Sight Base but not too much, fitting will be done when it is time to weld RSB on to the new receiver.

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Old 02-28-2010, 11:34 PM
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2.6.0.0 Salvaging Reinforcement Plate for rear push-pins (and stock pin sleeves)

Update 3/6/2010 : These are offered new by member Blackwing on MilitaryFirearms.com HERE.

Most builders do not pay attention to the reinforcement plate and some not even to the stock pins. I have not seen a factory HK without this, therefore I will include this. However this is totally optional.

There are a few ways these parts can be salvaged from a demilled receiver, but it is a tedious task. Sleeves are freely available, for the reinforcing plate you can cut a sheet metal to size and then fold/form it yourself.

Slit the top of the receiver. Then bend each side, you can now spread and open the receiver stub. Each side has three spot welds, mill the material off these spot welds almost down to the thin inner plate.



Open the receiver up and pop the spot welds. Secure the sleeves in a vive and further bend the receiver.



Cut off the excess receiver and mill/cut the remaining excess metal. Clean up. The pin sleeves are welded in, leave them as is.



Now using a press (or any other method) straighten out the Reinforcement plate. The sleeves are meant to stick out a bit as they go flush with exterior of the receiver, so it gets a little tricky. This one came out as good as new.


Last edited by fredieusa; 03-06-2010 at 9:17 PM..
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Old 02-28-2010, 11:35 PM
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2.7.0.0 Salvaging Paddle Mag Release.

Most likely the Paddle Mag release you have with your kit is the old style. At this point, you can choose to upgrade to the newer Anti Rattle Mag Release. You can use the same one for the 91 and 93, however the 94 (9mm) ones are different.

http://www.hkparts.net/shop/pc/viewP...6&idcategory=0

If applicable, remove the mechanism.



Cut along the rear of the Mag well, right on top of the structural welding. This will part the Mag well and you will need to pry it off till it comes free.

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Old 02-28-2010, 11:35 PM
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3.0.0.0 Parts Conversion to Semi-Auto

UPDATE on Semi-Conversion Jan-2010: I ran across this latest list issued by the BATFE- Technology Branch, that certifies an imported HK as a Semi-Auto. These new featured added or modified are far beyond what original factory Semi-Auto HK’s came with. All Semi-Auto features listed in this thread maybe something that is now required, I just don’t know. Build documented here was completed prior to the existence of this new list. http://hkpro.com/forum/showpost.php?...0&postcount=29

Below mentioned conversion is what was very much acceptable and very effective. Should you have questions and wish to explore more on this topic, please start a new thread here or on HKPRO.com. Shooting off letters to ATF for clarification leads to more confusion, more questions and still new rulings. This new letter linked above is a direct result of someone questioning some designs and features the new imported HK hold! Another example of outcome from writing letters to ATF is the broader expansion of 922(r), previously (for states where it is allowed) NFA items were exempt and now the ruling is reversed to incorporate ALL firearms, so lay-off on them letters.

Although I am going through this process of conversion for documentation purpose, I will NOT use the original Sear, Hammer and the Trigger. For compliance with 922(r), these (along with some other parts) will be replaced with US Made ones.

http://www.calguns.net/calgunforum/s....php?p=3661642

http://www.hkpro.com/index.php?optio...opics&Itemid=5

http://hkpro.com/forum/showthread.php?t=117946


I am doing all modifications for semi-auto conversions that are possible. Most people do not do all that I am demonstrating here. AGI Video does not limit the trigger travel by installing a new pin, but place a weld on the exterior housing that limits the swing of the selector itself. Few builds do not perform the Hammer notch modification, yet some do not bother with the lower trigger step that engages the sear. Many like to leave their bolt carrier as-is and not cut the notch for the clearance of the trip lever.

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Old 02-28-2010, 11:35 PM
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3.1.0.0 Eliminating Select Fire parts.

These parts will not be used, they should be disposed off.
Sear Catch and the Trip Lever are two parts whose only purpose is to facilitate select-fire capability, they need to go.

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Old 02-28-2010, 11:36 PM
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3.2.0.0 Trigger pack housing / body cutting and welding.

I cut the housing and thereby eliminate the location (pivot hole) where the Sear Catch and spring pivot. This modification will also allow the modified housing to fit only in a semi-auto grip frame. My method is not the simplest, fastest or the easiest; however it is the same as the original factory. The easiest (and still 100% functional) would be to simple cut out the scribed portion and move on to the next step.

Scribe lines along the top and rear of the pivot holes on both sides. Keep lines completely vertical and horizontal in relation to the housing, so the cuts are neat and in proportion. Make cuts on both sides of the housing and fold them out. Bend at the front as shown; it is important that the front corner created gets a square shape. If it is not square enough, it will not fit into the outer grip frame. I make use of a press to form the edge.



Now I cut off the excess ears. Smooth and bevel for welding. As I was too lazy to set up TIG, I use a jeweler’s torch with no filler. It got the job done just fine. Quality of the job solely depends upon an individual’s skill with the tool.



Note: One does not need to cut, bend and weld as done above. You can simply cut, as long as the external dimensions are the same. Here is a sample.

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Old 02-28-2010, 11:36 PM
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3.3.0.0 New pin location for Sear Spring.

Determining the hole location is important as it will determine the clearance for hammer and how effectively the sear spring works. Having drilled to some measurements offered by companies and individuals on the net, I find it easier to stick with the location that the factory semi-autos have. However, you will need to bend the sear reset spring just like the factory semi-autos (covered in the next step below) so the spring itself does not touch the sear, only the roller should come in contact. The bow-toe bending is not required, but can be included (added to) if your initial bending does not accomplish required results.

Vertical reference line (in Blue) is in the center of the pillar as shown.
Horizontal Line is 6mm parallel to the bottom edge.
The hole is drilled with a 5mm drill bit and then reamed.





3.3.1.0 Bending of the Spring.

Bend at the base where the spring coils around the pin. After a successful modification, only the roller should contact the sear thought its movement.



Just In-case the spring need to be shortened further, the angles at the bends can be decreased.



Do not forget the bushings during reassembly. These bushings will take up the space vacated by the sear catch which is required to be discarded.

I have seen semi-auto spacers for sale in the past. If someone has a link, please let me have it and I will add it here.
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Old 02-28-2010, 11:37 PM
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3.4.0.0 Internal Trigger Stop Pin.

This procedure is done to limit the movement of the trigger or decrease the length of the trigger pull by only 2.5mm (roughly 0.1”). This can be done by two ways.

First Method: Moving (or installing new) pins inside the pack that will result in decreased distance between the two. Or simply place a bead with a welder just below the upper limit pin and adjust as needed using a file.



Second method: Welding an extension on the trigger surface (shown below in pic) itself that will limit the travel upwards.



I limit the trigger travel by installing a new pin and eliminating the old one. The old one can be left as is, but it serves no purpose.
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Old 02-28-2010, 11:37 PM
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3.4.1.0 New Pin location.

Factory HK Stop Pins are installed 1” from the bottom (or about 0.52” from the top) of the housing and .84” from the rear. The diameter of the pin itself is 5mm. For our conversion, locating this exactly is not feasible (as-is) as it will require drilling over the circumference of the existing pin. So first I cut off the old upper limit pin flush with a Dremel (knocking it out can dent or disfigure the housing). While measuring for dimensions, bear in mind that the rear edge is curved so place a flat surface along the rear to accurately locate the spot.

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Old 02-28-2010, 11:37 PM
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3.4.2.0 Drilling for the new pin.

The pin should come from the same drill used for the drilling as it will be a good fit. You can also use anything in between 3/16”–13/64”, they will all suffice. It is very unlikely the Sear will not release the Hammer because the pull is not enough. Should that situation arise, that can be easily fixed by filing on Trigger arm that contacts the Trigger Stop Pin, being installed here. The old Stop can be cut off, as I have done below. Most builders leave the first pin as is, which is fine too.

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Old 02-28-2010, 11:37 PM
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3.4.3.0 Installing the new Stop Pin and securing with a weld.

I started to weld with the drill inside. Once the base was welded, I cut off the excess drill on the outside and cleaned off the rest. Here it is after a little dressing.



Notes: Many semi-auto conversion kits on the market come with directions that call for a 1/8” (3.18mm) diameter pin to be installed. They locate the hole where the diameter is located just outside of the existing pin. That is fine too, in-fact it is less work.
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Old 02-28-2010, 11:38 PM
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3.5.0.0 Hammer Work.

Eliminate the first notch / step as shown . This will eliminate the capacity of the sear to catch there. Factory Hk’s also have this done to their hammers.



Hammer is a vital part of your FCG. Smooth operation is essential. All surfaces that I worked on are buffed out smooth to a shine.

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Old 02-28-2010, 11:38 PM
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3.6.0.0 Trigger Work.

Grind out the lower step on the trigger as indicated with the arrow. I do this by cutting or milling straight down using a mill. It can also be done with a Dremel. This step ensures that the sear rests on the trigger in Semi-Auto mode only.

Note: The semi-auto notch should not be recessed in anyway. Under normal operation, we only have about 1mm of the trigger make contact with the sear!

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Old 02-28-2010, 11:38 PM
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3.7.0.0 Converting the Trigger pack housing / Clipping and Pinning.

Most people simply crop the ears off as shown. This takes away the ability of a semi-auto housing (with the ears cut off) to be able to mount on a full-auto receiver due to the lack of holes for the pivoting pin. Below is an example of what a simple clipping job accomplished and how it fit. Further on in the chapter I will be doing the shelf also.



Recently people have modified designs that appear like the original while maintaining features required for a legally defined semi-automatic. This relatively new process is called “Clipping and Pinning”, in addition to installing/welding the shelf that rests on the Receiver’s Semi-Auto wedge. Few posts down i also do this for kicks.


Last edited by fredieusa; 01-06-2013 at 12:54 PM..
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Old 02-28-2010, 11:39 PM
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3.7.1.0 Making a Semi-Auto Shelf for instillation on the housing. I was unable to find a shelf commercially, so I had to make one. A good shelf will block a G3 unmodified pack from being seated, yet engage the receiver wedge snugly eliminating any wobble or sloppy fit for the grip frame. My method was very labor intensive, given the availability of tools and material. There are easier ways, just bear in mind the goals we are trying to accomplish.



I worked on a chunk of bolt head that was severed while making a mandrill for another project. Shaping and grinding skills are elementary so I will not write a thesis on this. Not bad for only using the grinder and a Dremel.



It still needs finer adjustments and polishing. The final dimensions of the shelf I have ended up with are as shown in the pic below. I can polish and achieve the measurements mentioned above, but I find that unnecessary to achieve factory settings as done in the next sub-chapter.

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Old 02-28-2010, 11:39 PM
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3.7.2.0 Fitting the Semi-Auto Shelf.

Now that we have a shelf, its placement (in the housing) will determine how smoothly many other things come together. Again, mission is to maintain tolerances so we can interchange between factory H&K parts (if allowed by law, refer to 922r).

Here are some pictures from a factory H&K for reference for the steps below. As you can see, the factory shelf is a two piece item. Also the factory have relieved the housing’s lower edge back to the trigger guard tab.

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3.7.2.1 Vertical Placement: This determines two major relationships. Proper seating of the (A) Trigger pack, and matching with the (B) Semi-Auto wedge on the receiver.

A - If this distance is too little, the floor of the sear pack (as installed/welded in section 3.2.0.0) will hit against the shelf and will not let the sear pack seat properly. No worries about this gap being too large as long as the shelf lip itself is not too thin and the below condition is met.



B - Getting a reference point for this measurement is not as simple. This shelf lip will determine how snug the lower mates to the receiver. It should not to be too tight where it does not want to fit. If it is loose, it will create a wobbly and sloppy fit.

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Old 02-28-2010, 11:39 PM
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3.7.2.2 Horizontal Placement: Best is to line it up with the front wall of the housing suing a guide on the outside.

If this is placed too far back, it will not engage the wedge on the receiver or risk slipping off. Also you do not want it to touch (interfere with) the sear pack housing or the spring (as installed in section 3.3.0.0).

If the shelf is installed too far forward, it will create an unwanted gap between the trigger housing body and the receiver. Among other things (like hammer not making even/flush contact with the firing pin), it will lead to issues lining up holes for the rear stock push pins.

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Old 02-28-2010, 11:40 PM
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3.7.3.0 Welding the Semi-Auto Shelf.

H&K spot welded theirs on. Spot welds can be placed using a spot welder or simply welding the two locations and then cleaning it off will also work.

This is how the factory one looks.



Because of the shelf placement measurements in the previous section, I know where to drill in-order to get the solid sides of the shelf. To double check I scribe the inside Notice that the Trigger Guard slot falls dead in the center. Given the height of the shelf, I scribe on the outside, placing the housing against a level surface (curved edges are poor reference points). Now I have the top limit and the center line for my hole.

I locate the drill spot by dropping 5mm below the top limit line and punch it. I drilled 4.5 mm holes, this size is really a personal preference. H&K spot welds are about the same size. I clean the front half thoroughly with degreaser as oil runs towards the heat ruining the weld. Then buff out the park / paint from all four sides around the holes for a solid weld.



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Old 02-28-2010, 11:41 PM
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3.7.4.0 Clipping off the ears / Cutting off the tabs – Grinding the Tabs.

Cutting ears/tabs off. I do not cut the ears off because I went for the original type look, which gives the appearance that the push-pin is present. Reduction is done in section 4.2.3.0, when the semi-auto wedge is welded to the receiver.


Last edited by fredieusa; 03-01-2010 at 4:34 PM..
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Old 02-28-2010, 11:41 PM
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3.7.5.0 Installing Push-Pin bits.

This procedure is purely cosmetic, giving the appearance of the push pin being present. To prevent accidental release of the pin (not that it matters here lol), it is preferred that they be installed from the right to the left (It also depends on a personal preference, depending which hand the shooter shoots).

First I cut the Push-Pin head. Insert it all the way, scribe and cut when fully seated.



Now hold other end with wire lock held touching against the tab, scribe and cut. As the cut is made shorter than the point where the spring wire is anchored – it will come loose. I set the wire back in the pin piece and wedge in a nail to hold it in place. The nail will also act as filler so I can melt it and spread the material around, this will also secure the spring wire piece.



I can now either weld them or use an epoxy (after refinishing the housing), to secure the push-pin tabs to the housing.
I choose to go with welding. Epoxies are also very good and durable, it just so happens that my welder is all setup and ready to go. Place welds along the inside, grind to an even smooth finish.

Here the push-Pin head is welded.



Here the wire spring end is welded.



After a little buffing here it is with some slag still attached. Because I don’t want to scratch it or marr it, I will media/sand blast the rest of the slag off before parking.



Here is one commercially available. All ready to go, cuts down on time and money.


Last edited by fredieusa; 03-01-2010 at 4:34 PM..
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Old 02-28-2010, 11:41 PM
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3.8.0.0 Bolt Carrier.

This step is not completed by all builders. Regardless of this fact, I cover it. I have no idea if this procedure is required or even covered under any new guide lines. Please check on HKPRO.com boards or elsewhere on this. Again, don’t go shooting off letters to BATFE technology branch.

The rear of a Select Fire bolt carrier is complete, which facilitates the actuation of the Auto Trip Lever located on the right side when installed for operation. The trip Lever is already discarded from our sear pack as covered under section 3.1.0.0

The slot can easily be made with a Dremel. If you have a knee mill, there is nothing like it. The slot is 5mm wide and 6.5mm deep.

Before.



After.

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Old 02-28-2010, 11:42 PM
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4.0.0.0 Receiver building and completion.

Objective here is to get/build a receiver that accepts all standard accessories including different stocks. The bolt should not run too tight or have excessive play. The magazine should be easily inserted and held firmly, without excessive wobble.

4.0.0.1 Complete Receivers: There are a few available. On rare occasion, you can come across a FMP, but PTR are common as they are in production currently. PTR are VERY good! It makes no sense to bend your own, when one can get PTR complete receivers. It is cheaper to get the PTR, then to build one due to all the costs associated with building from a flat. Back when I got my flat, PTR receivers were not available.

PTR receivers are manufactured just like the original. Design and the process is the same, workmanship is the same. As you will see the amount of work and finesse involved in the following sections/chapters, one has to be nuts not to get the PTR.

Should you decide to get a complete receiver, you will still need to install the trunion and weld it to the receiver. The charging tube will also need to be fitted and welded. In short – Tools and skills required will remain the same, despite getting a complete receiver.



Cast Aluminum receivers are nice, but they do not readily allow acceptance of all standard parts. Aluminum receivers do work well and are just as durable, it depends on how they are assembled.

Myths: Aluminum receivers develop a play at the trunion.

Fact: Correctly assembled Aluminum receiver stays strong; the fit should be tight enough that a press should be required to push the barrel in. If the fit (@ trunion and barrel) is loose enough where you can push the barrel in by simply using a mallet (as shown in the AGI video) you are asking for trouble! If the fit is not correct to begin with (or the builder relies on epoxy or thread lock for a snug fit), how can one expect the receiver to last?

The retaining pins (installed on either side on Aluminum receivers) should also have a tight fit that requires a press. When installing a 4mm pin measure it. Also measure the drill bit that will be used for drilling the hole. Just because the drill bit if from a fancy company does not mean it is in specification.

I have a Springfield made clone in an Aluminum receiver, it is just as strong as any company HK out there.
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Old 02-28-2010, 11:42 PM
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4.0.0.2 Flats: Apparently all seem to work, despite where you get them. More appropriately; you can get all of them to work depending on your skill and understanding of the HK design.

Bending jigs: Knowing what needs to be accomplish is important as that will determine the process for bending/folding the flat. I have noticed folks (on the net) bend flats while holding them with a pipe, secured to a table using only adjustable pliers and clamps. On the other hand I have seen exquisite, Cadillac jigs custom made for the job.

The jig I use below is very solid, simple (to the point) and adequate to get the job done. It can be used with 9mm, .223 and the .308 flats. It has a lot of mandrills and rods to bend and adjust the receiver to correct some issues that may arise. I paid extra and got the rail squaring set-up also. This set-up cost me about $500.00 including shipping and insurance.

You can order these jigs DIRECTLY from the Original Source - Bob Nicholls, e-mail address is flatsolutions@yahoo.com
Bob is a nice guy and here to stay. Deal with confidence.




Addition : 06-23-2011 below..
New Jig on the market..

.

Guys just an FYI...

I saw this on GB and was in contact with the person manufacturing them.. I am NOT in the market for one but this product seems cutting edge. No need for a press and such. i think it offers the best control of the flat being bent and provides for much finer adjustments that may be needed. I have have built a few in all calibers and i think this is the finest one out there yet!

The seller seemed like a very nice guy too.. His e-mail is "sales@dauerhaft.com" <sales@dauerhaft.com>

Check it out here .. check with him for a GB
http://www.gunbroker.com/Auction/Vie...Item=221792709






Last edited by fredieusa; 06-23-2011 at 10:21 PM..
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Old 02-28-2010, 11:42 PM
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4.1.0.0 Bending the Flat.

4.1.1.0 Squaring the rails

After some experience, I find squaring the rails before bending is ideal. It is a straight forward process where I can apply adequate force precisely where I need; this leaves all stampings crisp receiver alone without flattening them out or placing stress on areas that are not associated with rails. There are exceptions where using a mandrill after welding may be necessary. That is covered in section 4.2.1.0.

The bolt carrier runs on rails formed / pressed into the flat. On most flats the rails come rounded, whereas on the original design they are sharp. Proper formed rails (to the original specification) will allow the bolt to function properly and also allow you to install the A3 telescoping stock. Here is a picture of a factory receiver, as you can see the corners are sharp.



Apply grease to both sides to prevent marring, level the flat (square it out) in the die and press with the mandrill to form a crisp / sharp rail edge. It requires considerable amount of pressure and working back and forth several times on both sides



Here you can see the before and after.





Squaring rails will straighten the main bulge in the flat, this is bad as it will result in the rails being too close after the receiver is bent and welded. Apply even force on either side when the flat is in the rail squaring jig till you get the same semi-circle form before you started.

NOTES: Squaring the rails is not required to get the bolt to work or the rifle to fire. Front of the rails (where rails meet the trunion) can be filed to match up with the trunion so the dolt head rollers can smoothly lock up in the trunion. More on this later in section 4.3.2.3 and 6.2.0.0.
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Old 02-28-2010, 11:43 PM
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4.1.2.0 Forming / Bending the flat

The flat is held square between the base of the jig and the mandrill by guide pins at both ends. It is vital that the flat is evenly placed in the jig. I measure (to the last fraction of a millimeter to make certain the flat is even. If the flat is not even, it will be lop sided resulting in a canted receiver (the mother of all many very serious issues).



Once the flat is bent a little, I check my measurements again to make certain that the flat is still even. It is not uncommon for a flat to slip and start to slide on one side (this will happen if your mandrill is not centered).

Go slow and press at different locations by moving the ram. It does not take that much force to bend, however it does require good technique. As simple as it looks, it must not be rushed. There is nothing you can do if you end up with a warped receiver.







If the receiver does go wrong (Canted or warped) at the end of this process, just start with a new one rather than trying to fix the error. G3 flats are complicated and will lead to newer issues in the process of trying to fix errors.
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