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Squirrel-tactical
12-11-2011, 12:27 PM
So I built a Bulgarian AK-74 from a kit. Bent the flat, drilled holes, heat treated, everything.

I took it to the range and put about 500 rounds of surplus 7n6 through it. By the end of the day I was noticing more and more malfunctions, until finally the top cover popped off. Upon inspection, I found that the rear trunnion had backed out of the receiver by about an eighth of an inch or more, and the receiver was bending away from the trunnion at the very rear edges. All of the trunnion rivets except one seemed to be in place. The 4th one (right side, forward) had dragged through the receiver steel, creating a gap. Does anyone know what could be causing this? My first thought was that the receiver flat came from a bad batch of steel, but now I'm thinking it may be over-gassed.

I've hammered the trunnion mostly back into place, but I'm still thinking of a way to fill the gap by the rivet. I'll post pics if necessary.

Thanks in advance.

joe_sun
12-11-2011, 12:40 PM
Was it a US made barrel? I know quite a few of them had oversized gas holes and it caused this exact issue.

wash
12-11-2011, 12:41 PM
That sounds like it might be two problems, a very over gassed setup and probably a receiver that was not heat treated or even completely annealed after bending.

It's not safe and you might get a bolt carrier to the face if you keep shooting it.

If the rivet holes are egged out, your receiver is done.

You can check the gas port using drill bits as gauge rods to see how big it is.

If both are problems, send it back because it's dangerous and probably not worth fixing.

Squirrel-tactical
12-11-2011, 12:51 PM
I was told the barrel is a Bulgy. Trigger-pin holes were heat treated properly.

Could I find a stiffer drive spring to help?

wash
12-11-2011, 1:03 PM
Since your trigger pin holes are not the ones that are causing problems, heat treating them doesn't matter, but while we are on the topic, tell us how you heat treated the flat.

A bad recoil spring could cause a battering problem I guess.

I still wouldn't fire it if your receiver has egged out rivet holes.

I shouldn't have said send it back in my other comment, I saw a similar problem posted about an IO or Century AK and was not thinking you had kit built this one.

First thing, get a new flat and rivets. Second thing, check the gas port size on your barrel. Third thing, read up on heat treating.

If you don't quench your steel immediately after heating it to red, you are not going to harden the steel, then you have to make sure you don't go too hot when you temper it.

It's easy to screw up if you don't know what you are doing.

Squirrel-tactical
12-11-2011, 1:16 PM
Did it at a build party under supervision. Head treated the rails and trigger pin holes only. Used a handheld blowtorch on each part till it was red then dunked it immediately. Are you supposed to head treat the trunnion holes? Because they weren't having us do that.

scotthmt
12-11-2011, 1:38 PM
rear rivets werent set properly. You need to get it on a press and re set those rear trunion rivets. Then i'd say probably get a mig welder and weld a small spot from the trunion to the receiver on the inside of the receiver.

Or you could tear the whole thing apart and rebuild it.

The choice is yours.

Squirrel-tactical
12-11-2011, 1:46 PM
Sounds a helluva lot easier than rebuilding it. Thanks.

m03
12-11-2011, 1:51 PM
A bad recoil spring could cause a battering problem I guess.


Worn out recoil springs have been known to cause the carrier to hammer out the rear trunnion over time, but I've only read about this happening on well worn rifles / kits (ones that have had a round count in the 50k+ territory).

joe_sun
12-11-2011, 2:39 PM
Were the holes for the rear trunnion properly countersunk or just drilled out so the swell neck rivets sat flush?

Also Wash, even thou I'm not super knowledgeable about flats, back in the olden days when Weezil_boi, myself and others held the first Sacramento build party, I don't remember anyone hardening the trunnion holes, only the FCG holes.

Man that was back in April of 2008 when Rommy kits with barrels were $99.00, my excellent condition Bulgarian AK-74s kit was a ripoff at $350.00 and my unfired Tantal kit was $200.00. $200.00 for a kit was crazy money since just a couple years earlier you could get Rommy kits for $70ish bucks each.

Squirrel-tactical
12-11-2011, 2:46 PM
Just so they sat flush.

Does the proper way involve countersinking the actual trunnion? Because I don't recall if they were already countersunk before I mounted it and countersunk the receiver holes.

ke6guj
12-11-2011, 2:50 PM
the proper way involves dimpling the holes in the receiver so that they interlock with the trunnion's beveled holes. If you just drill a countersink bevel in the receiver so that they rivits sit flush. those rivits have a swell neck for a reason.

joe_sun
12-11-2011, 2:52 PM
Just so they sat flush.

Does the proper way involve countersinking the actual trunnion? Because I don't recall if they were already countersunk before I mounted it and countersunk the receiver holes.

Check out this video, you only have to watch until you get to 1 min 40 seconds.

http://www.youtube.com/watch?v=x3OOPoQVGfM

This is what I'm talking about, the receiver needs to be "dimpled" into the trunnion.

If this wasn't done that's probably your problem.

luckystrike
12-11-2011, 3:01 PM
THIS is why I won't build.

Squirrel-tactical
12-11-2011, 3:16 PM
Ok, I see what you guys are saying. Pardon the confusion. I DID dimple the receiver correctly. However, I remember there being an issue with which type of rivets were being used, as I didn't have a full set (I had enough, but some were mismatched). I'm guessing I put an improper length one in.

I should be going to the Presidents' Day build, and I'll be bringing plenty of rivets in case that happens again.

SJgunguy24
12-11-2011, 5:18 PM
That gun should be rebuilt IMO. Who said the barrel is Bulgarian, is there military proof markings? The only thing I can think of that would cause the bolt carrier to hammer out the trunnion is the gas port's oversized, weak action spring, soft rivets.
Spec for the gas port with a 90deg gas block is .077" with a slight chamfer. Pull the gas block and check. You really don't need to pull it, just pop the pins and hammer it over 180deg, there's a hole in the bottom of the gas block that will allow you to see the port.

tujungatoes
12-11-2011, 5:19 PM
Ok, I see what you guys are saying. Pardon the confusion. I DID dimple the receiver correctly. However, I remember there being an issue with which type of rivets were being used, as I didn't have a full set (I had enough, but some were mismatched). I'm guessing I put an improper length one in.


I should be going to the Presidents' Day build, and I'll be bringing plenty of rivets in case that happens again.

sounds like you got some sh*tty rivets(tapco?). Many an AK has been built without countersinking or dimpling the rear trunnion rivets. They still shouldn't be hammering out. Generally when I've heard about this you end up finding out that the rivets used were caca.

Got some pics? Did you build this at one of our BP's?

THIS is why I won't build.

Stop being a wuss and build an AK.:p When done with the right parts, tools, and techniques you can turn out some really sweet guns.

Squirrel-tactical
12-11-2011, 5:28 PM
I don't have the gun on hand right now but I will take pictures as soon as I can.

A friend of mine actually bought all the parts online, so I can't confirm, but I believe he got the kit and barrel from Atlantic firearms and the flat and rivets from Ak-Builder.

And yes, I built it at a calguns party a couple of months ago. As it was my first build I tried to ask for help as much as possible and pay careful attention to any instruction I got, either online or in person.

Squirrel-tactical
12-11-2011, 5:35 PM
And I'll check the gas post dia as soon as I can.

nick
12-11-2011, 5:48 PM
THIS is why I won't build.

This is why I build - so that I know everything was done properly :)

Panchira!
12-11-2011, 6:16 PM
Hmm that is odd maybe the rivits were not set right? I would suggest you buying the parts so you know 100% what you have!

I build because I like that type of work, also I have seen off the shelf quality and it's sad. Like the old saying goes: if you want some thing done right you have to do it yourself.

Squirrel-tactical
12-11-2011, 6:24 PM
I just bought another 74, same setup, but this time I'm sure of what I got.

CSACANNONEER
12-11-2011, 6:46 PM
THIS is why I won't build.

At least you know what you are not capable of. Of course, There was a thread here about an 8 year old building his own rifle and, I've helped more than a couple of kids and adults build who have had almost zero experience using any sort of tools. Hell, we've even had one armed builders at build parties. But, it's good that you know your limits.

SJgunguy24
12-11-2011, 7:30 PM
This is why I build - so that I know everything was done properly :)

Exactly. I pulled out one of my garage builds and after looking over the rivets, I demilled it, those would not pass for a customers gun. One of the guys said they looked fine, well not to me. My QC tends to be a little more discriminating then what i've seen in some "factory" guns.

Shady
12-11-2011, 7:33 PM
At least you know what you are not capable of. Of course, There was a thread here about an 8 year old building his own rifle and, I've helped more than a couple of kids and adults build who have had almost zero experience using any sort of tools. Hell, we've even had one armed builders at build parties. But, it's good that you know your limits.

PWNED!!!

SJgunguy24
12-11-2011, 7:37 PM
PWNED!!!

I didn't have the heart to do it.;)

NorCalK9.com
12-11-2011, 9:00 PM
THIS is why I won't build.

C'mon you serious?
I've seen factory guns blow up in people hands yet I still shoot!
I've seen cars crash n kill people, I still drive!
I saw planes get hijacked and crashed, I still fly!
Etc etc etc.
See one of my rifles ive built and you'd say otherwise.

luckystrike
12-11-2011, 10:05 PM
At least you know what you are not capable of. Of course, There was a thread here about an 8 year old building his own rifle and, I've helped more than a couple of kids and adults build who have had almost zero experience using any sort of tools. Hell, we've even had one armed builders at build parties. But, it's good that you know your limits.

Well I sa.... Oh wait, I see what you did there, you are trying to be a dick. When I said "this" I mean I don't want to have to build 1rifle 2 times.

luckystrike
12-11-2011, 10:07 PM
PWNED!!!

Starting Internet fights. Not really.

CSACANNONEER
12-12-2011, 7:07 AM
Well I sa.... Oh wait, I see what you did there, you are trying to be a dick. When I said "this" I mean I don't want to have to build 1rifle 2 times.

Even that can be fun if you enjoy building things.

nicoroshi
12-12-2011, 9:46 AM
This is why I build - so that I know everything was done properly :)

Likewise :D
I have seen some of the 'factory built' IO Inc guns.
Scary

And for the OP,
My money is on the weak recoil spring
Even if the hole in the barrel is oversized the piston will only get the amount of gas allowed by the hole in the gas block.

Squirrel-tactical
12-12-2011, 9:59 AM
I'll have to test it against my new one and the one my friend just ordered, but I wouldn't be surprised if the spring was weak.

It's probably a combo of everything that's been mentioned though. I wish I could compare it with my friend's 74 that he built right next to mine, but he's deployed and has only put about 50-100 rds through his.

FiveSeven
12-12-2011, 10:17 AM
Likewise :D
I have seen some of the 'factory built' IO Inc guns.
Scary



I wouldn't call anything made from old surplus part as a factory built. Or anything made in U.S for that matter.

nicoroshi
12-12-2011, 12:17 PM
I wouldn't call anything made from old surplus part as a factory built. Or anything made in U.S for that matter.

Fair enough
Production, and company built then :p

My point is they are sold in stores, built on new receivers, and advertised as GTG when really many of them are not.