Heckler & Koch G3 Build

[fredieusa]

4.2.1.4 Magazine Well

Magazine Well – Should be 1.1500” / 29.2mm wide. Best way to check fit is to insert a magazine. The walls are bent, preventing the magazine from being inserted. In-fact the edges are so sharp they tend to shave the magazine.

To straighten out the lip do not use a players or similar tools, they will distort the edge which looks very ugly. Instead use a backing plate that can only catch the lip and not the bulged reinforcing stamping.



Press both side by placing a solid flat surface on the outside that runs through. The support on the inside (where the ram presses) can be smaller than the Magazine well, just move it around back and forth.



Now the magazine fits perfectly, without any wobble. It is held tightly and securely.

Next I inserted the BC group (while firmly pushing in the magazine with one hand) and noticed that the Bolt Head barely touches the Magazine Follower but clears both sides of the feeding lips – This is perfect.

To correct magazine depth into the receiver, apply procedures mentioned in section 4.2.1.1 and 4.3.2.2.

[fredieusa]

4.2.1.5 Stock / Back Plate Mounting

Attach the lower trigger housing and try to fit the rear stock (Back Plate Mounting) on. Most likely it will be very hard, use a mallet. Receiver height measurement at rear end – About 2.6400” high. This height can be adjusted by either pinching the receiver or by squishing it as described in sections 4.2.1.1 and 4.2.1.2.

If the Back Plate is mounted and holes do not line up, they can be adjusted. Hole can get misaligned because of procedures that were followed in section 4.2.1.2, but they will not be off by much. In the picture below you can see that three holes are fine but the fourth is off by 1.5-2mm.



The misalignment can be easily corrected by running a smaller diameter rod (which will barely fit) through the holes and press them into alignment. Correcting a 1.5-2 mm alignment issue does not distort anything out of specification that will impact other functions.

[fredieusa]

4.2.2.0 Magazine Catch

Notes: It is important to understand the relationship between parts before any adjustments are made. Top lip edge on the magazine anchors on the magazine catch, locking in the magazine at a specific depth into the receiver. Magazine catch rests on the lower edge of the magazine catch window of the receiver. Excessive trimming of the lower lip of the magazine catch window (of the receiver) will move the catch lower, resulting in the magazine locking lower in the receiver.

At this point the magazine catch holes are undersize, that do not accept the parts. The catch window itself needs work to accept and seat the catch properly.

Both holes for the Magazine Catch are under size. Enlarge left hole with a 6mm / .2360” drill. Enlarge the right hole with 5/16” bit as it also accommodates the contact piece (which goes over the Magazine catch arm).



After I inserted the magazine into the magazine well, I take note of the locking edge on the magazine lining up with the upper edge (of the catch window on the receiver) perfectly.



I tried fitting the magazine catch but the receiver prevents it from proper seating. Trace a precise outline and trim, being very-very precise on the lower edge of the window.



Still does not fit, needed just a bit more shaving. I used a hand file as I really wanted to go slow till I got it to seat. I don’t want to rebuild this surface using a welder.



Now I fit all pieces and make certain all is functioning well. Also insert a magazine and notice how it seats and locks.

[fredieusa]

4.2.3.0 Welding the Semi-Auto Wedge (Shelf).

As I have set the shelf on the Trigger pack housing to factory specs, the simpler way was to place the receiver wedge at factory specs too.

The factory wedge on the receiver is set at 1.4200” (X – shown in the picture below). Referring back to section 3.7.2.0 and 3.7.3.0; the grip frame measures 1.3880” / 35.25mm, this difference exists for the compensation and contour of the receiver.





Now that I know that the shelf needs to be at 1.42” below the receiver designated line, I prep up the shelf and measure both sides to be symmetrical (this also levels out the shelf).



I weld the bottom heavily. I weld the remaining edges lightly. Make certain that the welds are not obstructing the path or the surface while engaging the Trigger Housing.



Now I decrease the width of the shelf to match the trigger housing (also see section 3.7.4.0).

[fredieusa]

4.2.4.0 Welding rear Push-Pin support and sleeves.

This plate (spacer) is offered in new by Blackwing on MilitaryFirearms.com HERE.

Some builders simply weld the bare receiver and that works well for them. Below steps are not required for the gun to work. Here is what a simple receiver weld looks like. It works well by simply pushing pins in after installing the lower Trigger group housing and the butt stock end cap.



Although they are not required, they are surely desired. I start by enlarging the pin holes to .400” Then I place the demilled reinforcement plate (see section 2.6.0.0) with push pins inside the receiver and secure in place using a clamp.

As long as the outer receiver surface levels with the push pins, I am in specification to fit the lower Trigger pack housing.



After welding to match the factory, I clean the welds off and grind flush the bottom outer surface. In case the holes do not line up with the Butt Stock end plate refer to section 4.2.1.5. In the picture below the bottom needs a little more grinding to be flush plain.

[fredieusa]

4.3.0.0 Welding / Installing the Trunion (barrel), Charging Tube and Rear Sight

There is a unique relationship between the Trunion (that has the barrel and Front sight), Charging Tube and Rear Sight. Before I weld up any part, I mock up and check for fit and correct alignment.



4.3.0.1 Preparing the Trunion

Clean the Trunion for any oils and grease. I use liquid Tide laundry detergent. Degreasing facilitate good welds.



Buff out any material left over from the spot welds on the trunion that may obstruct the trunion from being inserted smoothly. Do not over clean or polish Trunion surface as that may decrease the size, which may result as a wobble or play when inserted into the receiver before welding.

[fredieusa]

4.3.0.2 Preparing Charging Tube

Bevel the inside of the cocking tube as shown in the picture below. The edge should be round and not marred. This beveling will allow bolt carrier a smooth ride when in battery (if the reinforcement is not full length). Also bevel the edge where it will mate with the receiver for welding.

The edge should be perfectly round so it may mate with the receiver without any gaps.

[fredieusa]

4.3.0.3 Preparing Rear Sight

Mount all parts on to the RSB and locate a neutral setting. This means that I dial the windage and elevation to the very center of their higher and lower limits.

Elevation: The drum has a total of about 10 revolutions (360 degrees) that can be effectively used before the drum becomes too loose. Tighten the drum all the way and then loosen full five circles, this will allow equal amount of adjustment up or down. Special tool is needed for elevation adjustment. Fine needle nose pliers also work.



Windage: The windage screw has a total of only 5.5 full revolutions. After tightening it completely, loosen 2.75 circles (1 circle = 360 deg). This will allow equal adjustment, whether left or right. It is also easy to tell visually when the sight is centered on the base.

[fredieusa]

4.3.0.4 Setting up the Boresighter

This will be used later in lining up sights. Ideally use a boresighter that can be chambered (less chances of errors). Below I use a cheap NcStar, it is the type that fits on to the muzzle.

There are a lot of methods to make a muzzle laser boresighter accurate. If it is round, roll freely on a flat surface (after turning it on) like a flat table top and notice the dot projection on the wall, the dot should not wobble vertically. The dot projected should be traveling in a straight horizontal line and not up and down. If the spot travels vertically, the boresighter needs adjustment.

I held mine in a drill press and marked a reference point on the floor. I made adjustments till the dot projected did not wobble upon rotating in the drill press.

[fredieusa]

4.3.1.0 Drilling Holes in receiver for trunion

[fredieusa]

4.3.2.0 Mocking-up Trunion and Charging Tube in Receiver

Here I use various methods to determine the ideal location for parts to match up. All steps are not mandatory, but I am not trying to spare any effort. I want this rifle to be accurate enough for hunting and target practice. Upon using premium loads, I want it to perform at an acceptable level that is expected with quality 7.62X51. If I were to spare details and effort, CAI $600 rifles would have been less work and far cheaper.

I start by inserting the Charging Tube into the Front Sight (triple frame). Then insert the other end and Trunion into the receiver at the same time.



Notice how the first edge rests on the Trunion.



If need be use a mallet simultaneously on the charging handle and the trunion to set into the receiver, as indicated by the arrows. I used a small plastic screwdriver handle through the front sight post to set the charging tube.



The trunion and charging tube should go in fairly easy with a mallet if receiver welds and Trunion were properly cleaned. Once in, the Trunion and Charging tube will be seated flush with the receiver.

Excessive gaps between the trunion and the receiver can be corrected by pinching the front of the receiver as shown in the next step 4.3.2.2.



Now match up the index on front sight post and the charging tube (as prepared in section 2.2.0.0).



The Charging tube will not be resting on the barrel. There should be a gap left between the barrel and the charging tube. More on this later, when I get to weld the charging tube in section 4.3.5.0.

[fredieusa]

4.3.2.1 Boresighting

Step 01 – Clamp the rifle (with the Trunion and charging tube pushed in) on a table or in a vice. It is imperative the rifle is straight (not tilted to either side). Should the rifle be tilted, we will end up with a canted sight. Pitched up or down does not matter i.e. vertical variations (up or down) do not matter. I use a regular water level to make certain the rifle will not be canted to either side. Reverse sides on the level to check for variances.



Step 02 – Rifle needs to be held firmly in place, but do not over tighten to the point that the receiver/Mag well is distorted or squished and not allow magazine to be inserted. Once things get welded, it will be very hard to tweak the receiver.

Pin up a sheet of paper opposite the muzzle. The distance really does not matter but it should not be too short. I have it at about 12 feet from the muzzle, we will be going by line of sight – not trajectory



Step 03 – Look through the barrel and make out the center spot on the paper through the barrel. Now mark a dot on the paper target that falls dead center when looking through the bore. This is visual Boresighting.



Below I mimic a misaligned trunion/barrel by not properly seating them to illustrate a point.

It does not take an expert to tell if the receiver is lined up straight when looking through the bore. In the picture below, it is clear that the receiver is NOT lined up correctly. With the bore centered in my vision, the rails do not appear equal. Clearly I need to adjust the barrel to the right so the rails will visually appear equal when I look through the bore. I made this correction in the next section 4.3.2.2.



Step 04 – Install the boresighter and turn it on. Rotate the boresighter in the muzzle and the projection should not move (also it should relatively be the same as the mark #1 already placed). If the projection moves, it will be in a circle around the mark that is already placed in the last step. Should the laser not be exactly centered on the mark, just take the center of the circle the laser makes itself or try fixing the laser (as explained in 4.3.0.4) but there is not a whole lot one can do if the arbor itself is kaput.



I use a level to draw a (true) vertical line through the first mark (from visual/bore sight). Now I place a SECOND mark (on the line - above the first mark) to compensate for the distance between center of bore and front sight blade notch. Place mark # 2 exactly 2.1010” above the boresighter dot. [0.4295” (0.8590/2 half of the barrel and part of FSB measurement) + 1.6715 (distance from the base of the FSP over the barrel to the tip of the blade)]



Now I have a verified line of sight for setting my rear sight. All I have to do is line up my rear sight assembly (complete) with the front sight and to the Dot # 2 on the wall. This determines the precise location at which the RSB will be welded. Verify the location again by turning on the boresighter and check that the beam is still set at dot #1while sights line up to dot #2.

[fredieusa]

4.3.2.2 Fixing Canted/Misaligned Barrels

Here I will list some procedures that can be used to correct the trunion and receiver fit. They can also correct slight gaps that may exist between the trunion and the receiver.

Trunion has raised surfaces where rails should rest flush.



Both rails should be in contact with the Trunion evenly when properly installed.



Reasons for the rails not resting on the trunion evenly are limited. No, it’s NOT the flat that is defective or designed/manufactured incorrectly! Rails can get uneven if mandrill was not evenly placed when squaring rails. Using undersize rod through the receiver when folding can lead to receiver to be uneven. This will leave small variations that cannot be corrected regardless of the use of clamps to level surfaces and match ends when welding (section 4.2.0.0).

Fix # 1 At this point, very slight adjustments can be made to correct misaligned Trunion (barrel) fit with the receiver. Use a press to apply force at the base of the barrel / edge of the receiver. The receiver and the barrel must be well supported so they do not bend or warp. The force should only affect the front end of the receiver that contains the trunion, forward of the rails. Shims can be used to support the barrel profile.

Use a solid rod instead of the charging tube. You don’t want the charging tube dinged up. My illustration in the picture below does not support the barrel and receiver as good as I have suggested above. If you do use this procedure, make certain they are supported well.

Excessive force will disfigure the receiver opening, ruining it. Well the rifle is ruined anyways because of the canted barrel if only iron sights are to be used. However the rifle can still be usable (if the barrel misalignment does not bother you) as long as target is acquired via mounted optics or a simple barrel mounted laser (boresighted at varying lengths) lol. This method can also be used to fix misalignments mentioned in section 4.3.2.1.



Fix # 2 The front end of the receiver can be pinched in using rods (punch shaft, screw shaft, bolt shafts and drills all work) that are small enough to fit into the groove. Receiver front end must be supported by the bolt carrier or the trunion (with a support like a solid rod for the bolt guide) itself. I placed the contraption is a vice and tighten away.

This procedure is highly recommended to eliminate any gaps that may exist between trunion and receiver when mocked up. It does correct alignments also but not as effectively as the one above. The smaller you keep the pinching rods, sharper the pinch. The supporting rod I use for the bolt guide has a tight fit, so I don’t have to worry about the charging tube extension not fitting.



In the picture below, I use the bolt carrier itself. Here one has to be careful as to not over pinch which may result in the guide tube extension not fitting. Also notice the use of drill buts instead of larger rods for pinching.



Now install the Trunion (barrel) and the charging tube back into the receiver as done in section 4.3.2.0. Things may fit a bit tighter, but that is expected. Repeat section 4.3.2.1.

Once everything is lined up, it is a good idea to insert the bolt carrier and see if it fits. With all the stress applied on the receiver, it is easy to get it out of specification. Should that be the case, refer back to section 4.2.1.1. and repeat section 4.3.2.1.

Now that everything fits and lines up, clamp the receiver and the trunion as it is easy for this setting to change with everything else going on. Locate the clamp where it grips the rear ring of the trunion, this keeps the front clear for welding (placing it in the center will dent the unsupported receiver). I keep the clamp in place till I at least place two welds later on in section 4.3.4.0.

[fredieusa]

4.3.2.3 Trunion and the Rails

The inner surface of the trunion should be flush with the rails so the rollers on the bolt head can transition smoothly. If the inner surface of the rails (that contact the rollers) do not line up with the trunion, refer to section 6.2.0.0.

[fredieusa]

4.3.2.4 Rear Sight Before making any corrections, it is important to understand what exactly needs fixing. If there is a cant, it can simply be the rear sight or the trunion not indexed correctly when pushed into the receiver. Refer to last section 4.3.2.2 for detailed fixes.

Here is another alignment test that can be done. Run a thread over the Front sight notch and straight to the center of the receiver at the rear (or the notch in the rear sight). The thread will let you know if there are any alignment issues.