Virgin Build AK-47 Yugoslavian M70AB2 Stamped Receiver Yugo M70 AB2

[fredieusa]

*****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. Also know all your laws, its amazingly easy to get into trouble with the CADOJ or even the BATFE. This thread of mine is for pure educational purposes. It is not my intention in anyway to get you to follow.*****

Virgin Kit = Parts that have never been assembled into a working firearm.

Here is a build for a Yugo Under-folder VIRGIN kit. For this build I have used a stamped/bent flat receiver. This rifle will be CA compliant, Detachable magazine capacity removed, fixed stock pinned open OR muzzle device attached so the OOL is 30" or greater.

For illustration purposes and the fact that I often forgot to take pictures, I will be using picture from other builds.

Features and regulations specific for California are NOT mentioned/listed, as i go along because it is also meant for some folks from other states.

Prerequisite: Meant for folks that have already completed a build or two from a de-milled kit. Have good mechanical skills, tools and pertaining knowledge.

I will be skipping over all (or most of) steps that one would go through (building and refinishing) while completing/building a de-milled kit. This means we will not be touching on Magazine fitting, mag catch and trigger guard riviting. Trunion fitting and rivitings, Painting/bluing or finishing the rifle (wood or metal). I have kept this build as simple as I possibly could, without the use of a mill or lathe!

This is the kit I will be completing... Bought back-in-the-day and it included the barrel, rivits and all.. everything but the receiver.


This kit will look like this when done.. I got the below photo from here http://akpartskits.com/cart/index.ph...&products_id=6 (not plugging them, I have no idea who they are, just used their photo so I thought I should list them..)
AGAIN this photo BELOW is NOT mine. Its from this web site. Yes the kit comes with FA parts that YOU/I discard/resell on GB.

[fredieusa]

Receiver and Trunions

Crimping/crushing rivits is the same as in the demilled kit so I will run over this fast.

Here the trunion holes were slightly small (for AKbuilder rivits) so I ran a drill through them.


Now install the trunions in the bent receiver and line holes up. For a Yugo M70AB2 you will have to drill an additional hole in the bulge of the trunion. Most receivers have the hole drilled so just center punch and drill away.

Here the receiver is almost complete with all rivits and trunions, including the Mag release/trigger guard and the pistol grip nut.
This came out pretty squared-up and decent.

[fredieusa]

Installing a "bullet guide".

If your trunion already has a bullet guide installed, you may skip this part.. (probably the only time you will install a bullet guide is when you decide to go with a different trunion (that is stripped/New/Virgin) or go with a new milled receiver that does not have one installed - like in this case below..) If your kit came with a TRUNION (sheet metal receiver kit/ Flat receiver kit), it came with a bullet button installed. So skip over to post # 8

There are different bullet guides for 7.62, 5.56 and the 5.45. You can reuse one from your de-milled kit





Now pressing in this rivit is a cake..



This is how it looks turned upside down. With the round rod at the bullet button face supported.



Now simply crush the rivit like this ..

[fredieusa]

This is how it looks crushed. in the photo below I meant to write diameter and not circumference. IOW twice as wide.




Finally the bullet guide is done!

[fredieusa]

Issue discussed in this post is very uncommon. i have encountered this only once before. Both times it has occurred on domestic MILLED receivers. If it helps you to know, they were on different makes, this pretty much covers the domestic milled market (other than Arsenal)

Incorporating this to "fix" your company made name brand is also not advisable as it will most likely throw off your head-spacing. These details are only noted by careful and detail oriented builders, others simply overlook.

As shown in the picture, the bolt does not contact/meet the receiver at the charging handle side. Shown with a blue arrow.
The point of contact is on the point shown by the red arrow.
The area taken up on the point of contact (red Arrow) is very small. Usually it is on the other side (opposite).

It is common to see bolt making contact with the receiver/trunion on the charging handle side. This gives a wider area for the continuous impact over long time.

IDEALLY, we should have the bolt touching at BOTH locations, but that is RARE.



The gap is about 1.25mm ( .0495" roughly) wide. I have decided to decrease this gap by shaving off both, the receiver/trunion and the bolt carrier. Here the receiver/trunion has some material filed off (about 0.6mm) Circled on RED



Here I noticed that the bolt carrier is slightly convexed out, so I make that area smooth (circled in RED). This gave me the other .6mm or so needed.

As I tried the bolt carrier, it still did not want to make contact at the desired location. The carrier was making contact with the receiver at an undesired location and that too was smoothed out - Circled in BLUE.



With a little more nip tuck (filing and polishing) I have even contact on BOTH points on the receiver/trunion!
This will help dissipate the pressure created by the constant pounding of the bolt during cycling.

I use a marker to confirm even contact.

[fredieusa]

These steps are imperative if you want a smooth action AK.
You can get yours as smooth as one that has been through 1000's of rounds
without wearing out the barrel, ejector, extractor or the firing pin.

Run the bolt head on the rails, there is a good change it will be stuck at the ejector. Use a file to get the area of the ejector down so the bolt head may pass freely. Be be careful not to over do it.
The whole point is to have the largest ejector possible while attaining a smooth clearance.


Now although it does pass very smoothly, it is slightly canted/pushed towards the selector side..
That means it may still snag if run complete with a bolt carrier.


So to make certain we have a smooth/snag free sliding of the complete bolt assembly, (past the ejector) we try it out.
Needed a little more tweaking.. but i got it just right.

[fredieusa]

Having installed the bullet guide we will check to see how it operates. It also assists in the turning (and locking) of the bolt head!
As the barrel is not yet installed, we have plenty room to get in and smooth things out with a file or dremel - if need be.

Again, we start with the bolt head alone and see now it rides into the locking lugs AND turn. The objective here is to achieve the smoothest ride possible while the bolt head rides (as far as it will go) up and locks into the lugs

All new bolt heads have sharp edges and corners. I used a new marker to lay a thick black coat on it so I will know the snagging points.


Note only the locking arms/lugs and their edges is where I am interested in ...


Here it rides in decent, (can easily get smoother)


And now it locks (turns about 20 degrees towards selector side).It took a lot of time and wiggling for it to lock and about just as much getting it loose. I repeated this step a few times to understand the relationship and snag points (each rifle is unique when you reach this step). I also have the black marker on the bolt head to aid me.


And here we get to see the highlights.

[fredieusa]

Never touch the bolt head face. Just the edges that need a little POLISHING..
I used my file very gently and here it is.

After repeating this process {of using a marker and filing the resistance points} about two times, this bolt head is rather smooth



I also had to fix/smooth out the receiver/Trunion




Here is the starboard side.
Note - I have smooth out the surfaces leading into the bolt head locking area but NOT decreased the locking lug face area

[fredieusa]

Now that its running smooth by itself, I will try it out with the carrier (just as we did for the ejector).
This is important as without the carrier, my fingers may adjust to tension and give the illusion of a smooth action. The bolt carrier will keep the bolt head in line.


Now trying with the carrier...


Not as smooth as i would like.. and so I take note of marks yet again.


But this time I don't use the file. I simply use a buffing wheel..



Now I will try it out again WITH the bolt carrier..AND the recoil spring..


You should not use the charging lever to check action smoothness as it cants the carrier and it WILL jam. as shown here..

[fredieusa]

The way I do it.. I place the piston against a solid surface and push the receiver body. This gets the piston moving straight, back and forth. You may also simply push down on the piston with one hand while holding the receiver body in the other.

Make note to observe the bolt head riding and locking smoothly...


And we have a smooth action ! Really!
To have a finished rifle that is really smooth, you will have to tweek the FCG (fire control group) also.

[fredieusa]

Barrel Instillation - Our barrel is white with no holes. Its a virgin too..

This section may also be referred to when changing out a barrel or installing a new one in any kit.
i.e. AMD kits come without original barrel.

Barrel Address / Markings. This is a matter of preference, I like all (or as many as possible) my barrel marks, proofs, bore info to be facing up. They should be visible as soon as the upper hand-guard is taken off. So I make that determination now as to which side is up.


Now for the extractor cut out.
The depth of this cut into the barrel is about .050" That is roughly the average I have taken.


BTW there are NO hard and fast rules on this cut. Use a grinder or a dremel. The smoothness comes with experience. You may want to practice on a metal chunk before destroying a good barrel. Here is a late model Bulgarian factory cut. This is what "the factory" is doing now.


The cut out should be wide enough to accommodate the area marked below on the bolt face. And yes, the bolt head does turn/swing to lock.


Another illustration

[fredieusa]

Now we move right along and take barrel - trunion measurements.

NOTE 01 - factory kit Yugo barrel and trunions are just right and do not need to be fitted. Fact is the M70AB2 virgin kits have all parts - RSB, Lower Hand Guard retainer, Gas block and FSB matched up and they dont need to be trimmed / turned down. Using another trunion (milled receiver in this case) may need fitting.

NOTE 02 - You will often see numbers stamped on your parts (FSB, BG, RSB, Trunion) ranging from 1 to 4. These are production limit control numbers and have nothing to do with quality or accuracy as some believe. This method of grading production is very common in any mechanical production shops. It tells the operators when to change out old tooling so the product remain within tolerance.

1 is for under-size, 2 for standard, 3 for over size and 4 for way over size. Parts were grouped accordingly and assembled.
The factory/Arsenal also mixes and matches parts so you may end up with a 1 and 2, its no big deal. This does not take away from your value or originality.


Here my measurements from the trunion come in at .8985"


And the Barrel at .9075. The difference is just too great.


Ideally the barrel should be turned in a lathe between the centers (using live center) so you may also check that the outside diameter is concentric. BUT we have to do this without a lathe.. so here goes..

We need to bring the difference between the barrel and the trunion/receiver down to .003 from .009. (The barrel stays slightly over sized). We do this by enlarging the trunion hole! Here are our $6 fixings that will replace a lathe.

Glue
Double sided tape
Drill bit anywhere between 1/4" - 1/2"
assorted Sandpaper


Using the material above, fashion yourself a drum sanding device that will barely fit into the trunnion. And sand away for 10-15 seconds at low speeds periodically checking the diameter... till you are done.

The sanding will self center as it moves as you are using free hand. It is important you do this with a hand held drill to make certain the material taken off is uniform!




Now that the trunnion and the barrel are within limits, we lube them up


Now you may start to press the barrel in - Have your extractor cut positioned right, eye blinking later will not help. You will have to press out and start over..

The smoothness of the barrel pressing will depend upon the tonnage of your press and how tight the fit between the barrel and the trunion/receiver is.

If you are using a 12T press and the barrel "bounces" forward instead of creeping (despite the use of lube), the fit is a little too tight. Or you may just use a heavier press. If your barrel-trunion fit is too tight (should you decide to use a heavier press say a 40T), you risk cracking your your trunion.

Cryogenic cooling and then pressing does not help. Also it may cause rust over time, as the moisture in the atmosphere freezes on the cold surface right away.

Headspacing is adjusted in fractions of a MM. If, with each bounce you move .5mm or more, it is no good.

[fredieusa]

This little step in the bullet guide (marked with red arrows) is where you need to push your barrel to. Keep it slightly shy if you can ~ .5mm


Here is a barrel pressed in roughly to that point

[fredieusa]

incorrect headspace gun going boom in at the wrong end ..
http://www.youtube.com/watch?v=rQep2nWGfBw


Now I correct and adjust the head-spacing. I have to determine whether the current head-space is small, large or correct. There is no such thing as almost correct. I use an assortment of devices to accomplish this.

Assorted make (DUMMY) cartridges with no powder or primer
Scotch Tape
Head-spacing gauges (not a must if you have the above - That's right)

The variation between a Go Gauge( in specification) and No Go gauge ( out of specification - larger) is only .0045" to .005"


Assuming we don't have go - no go gauges, we can create out own.
Three layers of the scotch tape adds roughtly .005", to a regular cartridge making/representing a NOGo gauge.
The regular cartridges, without any tape on them will suffice for Go gauge.

So here is our NO GO gauge..



Inspect your chamber first to be certain it is clean. With all the metal shavings and chips around, you can not be sure.

1 - Using No go gauge - Action does NOT lock, bolt head does not seat and lock - This is normal, move on.

2 - Using No go gauge - Action DOES lock - Head Space is too great. Barrel needs to be pressed IN a little more, you are doing fine.

3 - Using GO gauge - Action does NOT lock, bolt head does not seat and lock - Head Space is TOO tight OOps. Reverse the press jig and press the barrel OUT some. You over pressed it.

4 - Using GO gauge - Action does lock - Beautiful. we have correct head space. Repeat steps 1 and 4 with recoil spring several times.






It is tight headspacing that is more dangerous. It results in the cartridge making a tight contact with the bolt head without the bolt head being locked in place. Pulling the trigger does set off the round, causing an explosion 8" from your eyes, having enough energy to shatter receiver, strip the magazine or rounds by blowing out the mag floor plate. And all sorts of stuff that make good stories and conversation pieces.
Here is great video checking/fixing headspace.

http://www.youtube.com/watch?v=8HR3RnBNVTA

http://www.youtube.com/watch?v=KICBv-0U87Y

http://www.youtube.com/watch?v=3HfJFg81BuM&feature=fvsr

[fredieusa]

Pressing in the Rear Site Base (RSB)..

This RSB self centers on front trunion, as tolerances are tight. The receiver/trunion is 24mm even and the RSB width is 23.90mm

The barrel at the point (where RSB is going to slide over) is 18.6mm and the RSB hole is almost 18.55mm. Lube it up.


Push on the barrel and no where else. Remember, we don't have a BARREL RETAINING PIN YET. If you apply pressure anywhere else other than the barrel, you will be affecting/disturbing the HEADSPACE. I keep it this way so I can adjust for "cant" - Avoiding canted Gas block, canted Front Site Base FSB.



The RSB will stop once against the trunion/receiver, as shown with RED arrow. Again dont keep this tight. It may push on the trunion. Let go as soon as the RSB reaches there. Dont push on it.


Clean out the extra grease. It keeps the project neat and tidy, plus it helps with refinishing later. Check the RSB so it is square and not canted. If it is canted, get that 3 Lb. mallet out! You can also get creative and use a vice to correct the cant. Be careful not to ding up and marr the project.