Calling all seasoned AK builders!

[Eisenwaffe]

So, I finished my first ever AK home build a month or so ago. Took it to the range several times, ran like a top, no ftf no fte, etc. However, after my last outing, I returned home and noticed my rear trunnion has been pushed back 1-2mm, no longer flush with the receiver, and the two long rivets have been bent. The rear trunnion does NOT show signs of being impacted by the bolt carrier and my recoil spring does NOT seem slack or soft.

The rivet set I used on the build was from Toth Tool; I used their front trunnion rivet squeezer, and those came out great and seem to be holding perfectly fine. I did not, however, use their long rivet squeezer jig, I made my own backing plate and a homemade rivet die, and hammered them in, not squeezed.

Now my question is, could hammering them in, as opposed to squeezing, somehow weakened the rivet material enough to cause this failure? I remember thinking that they seemed very soft to begin with. I've fired maybe ~400 rounds, and recoil didn't seem to be excessive, like say, if the weapon was being over-gassed?

Again, it does not appear as though the bolt carrier has been slamming into the trunnion. Maybe I got a bad batch of rivets? Maybe my method of install weakened the metal? (the swell necks seemed to be seated well, and the rivets were flush)

Advice?

[hellayella]

who's ur builder...time for the pitchforks and torches!

[bigbob76]

My guess would be that you beat a head on the rivet without expanding the shank. When you use a press the whole rivet fattens up in the hole through the trunion. Also, were the holes through the trunion wallowed out oversized?

[valley82]

My guess would be that you beat a head on the rivet without expanding the shank. When you use a press the whole rivet fattens up in the hole through the trunion. Also, were the holes through the trunion wallowed out oversized?

This...although I am just a builder deffinitely not a master.

[kcstott]

This...although I am just a builder deffinitely not a master.

Yep my guess as well

[socom2shooter]

You probably didn't heat treat the whole reciever. Normally that stops this problem.

[valley82]

You probably didn't heat treat the whole reciever. Normally that stops this problem.

This I will disagree with as I have built in excess of 30 AKMs...3 of them were built on Nodaks the rest on flats with only FCG holes and ejector heat treated. All of them have plenty of ammo through them and I have had zero issues with anything moving, loosening or wearing on any of them.

[thedrickel]

Either your rivets are soft, or you didn't squish them enough.

[kcstott]

Nope not the issue.

Yeah maybe in a few years time after a few thousand rounds sure. but not a new weapon.

Incorrect rivet forming in a larger then rivet body hole. yep it's going to move for sure.

[CSACANNONEER]

bigbod76 nailed it.

[Eisenwaffe]

Thank you guys for all the input! It is my first build, it's been a major learning experience, and as such, I expected to possibly run into a few minor snags.

To answer the questions/provide more info.
- I was the builder, so I can only blame myself lol
- The rear trunnion was new, never been demilled, so I assume the opening isn't oversized.
- The receiver is an OOW 100%, fully heat treated

I'll drill out the rear rivets and give it a go with the press. I had heard of people hammering in the long rivets, and I figured it wouldn't be much different from using a pneumatic rivet gun, but I can definitely see how the consistent increasing pressure of squeezing the rivet would be more effective than a repeated impact to get the rivet to "flow"

Again, thank you all!

[kcstott]

Thank you guys for all the input! It is my first build, it's been a major learning experience, and as such, I expected to possibly run into a few minor snags.

To answer the questions/provide more info.
- I was the builder, so I can only blame myself lol
- The rear trunnion was new, never been demilled, so I assume the opening isn't oversized.
- The receiver is an OOW 100%, fully heat treated

I'll drill out the rear rivets and give it a go with the press. I had heard of people hammering in the long rivets, and I figured it wouldn't be much different from using a pneumatic rivet gun, but I can definitely see how the consistent increasing pressure of squeezing the rivet would be more effective than a repeated impact to get the rivet to "flow"

Again, thank you all!

you could use a aircraft rivet gun on every rivet but the long rear trunnion rivets. the reason is the rivet needs to be crushed back in the hole to fill out cavity. Then the rivet quits shrinking in length and the head will form properly

Just hammering it will form the head first and not provide a solid connection.

[6mmintl]

Maybe this will help

[kcstott]

Or this

[Eisenwaffe]

UPDATE!

ok, so I began stripping the rear trunnion from the receiver shell, and upon closer inspection (ie. cleaning off the trunnion really well), I can see signs of the bolt carrier impacting the rear trunnion. The rivets were being "cut" by the hardened receiver shell, despite the swell neck being fully engaged against the trunnion. There is zero play between the rivet shank and the trunnion holes, so it looks like my install method worked better than expected to squish, and expand the shank. pics attached.

SO, now knowing that the weapon is potentially being over-gassed, what can I really do other than get a new barrel? Note: I bought the kit pre-populated, so I had nothing to do with drilling the gas port! It's one of the 16" barrel AMD65 kits from Classic. Could having the shorter length AMD gas tube on the longer 16" barrel have anything to do with it?

Possibly vent the gas tube to let off some excess pressure?

And, as suggested above, I'd rather not weld the trunnion, simply for the fact that I want to correct the problem (over-gassing) not just Band-Aid it.