Hi, I built a Bulgarian AK-74 awhile back with some others, this one using a 5.56 barrel but hadn't gotten around to testing it much later (after I'd sold my build tools).  I read many threads about doing this successfully using the original 5.45 bolt (it's a bit loose but the extractor still grabs) and most people had no problems.

The build went smoothly, and the rifle fired and cycled ... however, once in awhile... about once per mag, it will eject a spent cartridge AND a live round in one cycle.  Sometimes it will pick up the next round, other times, it won't.  I also messed up heat treating the ejector and it chipped.. although it does still eject ok. Not my best build :(

When I did the build I found the 5.56 magazines (Bulgarian clear waffle mags, circle 10) did not fit. It seemed as if the trunnion was too high.  The feed lips were hitting the lower rails.  I did not want to grind away the trunnion, and there was not much of the locking lip to remove, so I just removed some material from the top of the mag lips (easiest part to replace... a magazine) to get the mag to seat. Hard to describe, so I've attached photos.

Rifle fired and cycled but occasionally stripped (or possibly fed) two rounds.

My first assumption was that I totally screwed up bending the flat, and that the receiver dimensions are out whack and the mag was sitting too high or lower rails too low. But after further investigation, the bolt is only in contact with the rim of one around at a time when stripping it from the mag, and it looks correct from the rear of the mag.

I looked again and noticed that the mag is angled... the front of the mag seems about 1/16" too high.  I think what is happening is that as the bolt strips the top round, the second round is getting stripped by friction, and the nose of the bullet is high enough that it is getting over the feed ramp.  This would describe the double feed or double eject (it alternates).

I *think* what I need to do is either try new mags, or dremel the front locking lip of the mag so that it sits lower (and aligned) in the mag well.

I figured I'd ask here before I give up and chop the receiver and sell it as a parts kit.  My other option was to buy a 100% receiver and rebuild the rifle... but at this point I'm not 100% sure it's the receiver and as I said before, I already sold my rivet tools and jigs.

Anyone else had this issue before?

My gut feeling is that I need to lower the front of the mag by removing some material from the mag lip, or try a different magazine.

Any advice appreciated.

Thanks!

Picture #4 shows the back of the magazine sitting to low. Is the support rivet stopping it?

No the support rivet is not stopping it, although I did just grind some of the support away to clear the mag and it helped a little.

I know it looks like the back is too low, but I don't think it is. I've seen some other photos of 5.56 builds and the mag looks a little tilted back the same way.

I'm going to try some other mags before I assume it's the build.

Notice the cracks in the clear mag.. they ALL cracked in the same place : |

I'm using the same mags with a Bulgarian kit and Nodak Spud receiver. The mags lock up tight and all the way up.
I had a 47 build that the mags set in too low in the back and wouldn't feed. I ended up replacing the mag catch latch.
Good luck with it

It does open up a can of worms when your receiver is home built, and dimensions cannot be guaranteed. My first thing I noticed was your ejector, but at least you seem to have no issues with cases leaving the receiver. The ejector usually does not play a part in double feed issues, fortunately.

My first guess would be that you managed to warp the front rib and feed lip section of the Bulgarian magazines. Back when I fitted a batch of Polish Beryl mags to my Saiga .223, I had this exact issue. I initially had to file some material from the section of the feed lips that contacts the bottom of the trunnion locking lugs, but I didn't remove enough material and caused them to lock in too tight. This caused the steel reinforcements in the feed lips to bend outward, thereby spreading the feed lips open a tiny bit all the way to the rear of the magazine.

The magazines would load and strip fine out of the rifle or by hand, but would often double feed while in the rifle. The slightly bent steel reinforcements allowed the feed lips to spread enough so that the stack was not being held tightly enough, and the shock of the bolt passing over the leading round would cause it to pop up out of the feed lips and jam up inside the receiver.

I took all of the affected mags, squeezed the reinforcements back into shape with channel locks, and removed a tiny bit more material so that the trunnion locking lugs would not put pressure on the reinforcements. They now run fine in the Saiga.

With the Saiga, I also noticed that the sharp edges of the bolt bottom lug were occasionally scratching/biting the case of the leading round in the mag stack. I very lightly chamfered the sharp edges of the corners on the bottom lug - you want to go easy on this as each bit of material that you remove results in smaller contact area with the case rim during the bolts' stripping of the next round. If your bolt has very sharp edges on the bottom lug here, just chamfer and smooth out the edge so that it doesn't bite the case.

I did NOT have to do the above with my 5.56 74 build.

NOW... I also have a build similar to yours, using NDS-2 receiver and Arms of America nitride 5.56 barrel. However I am not using Bulgarian mags with this one, I use Polish Beryl mags. I did not have any fitment issues with the mags - the Beryl mags that were modified for the Saiga, as well as the unmodified mags, snapped right in to the Bulgarian 5.56 74 build. None of the mags have feeding issues.

I also needed to tune the extractor on this build. The extractor seemed OK at first testing, but I soon realized that it was allowing the 5.56 case rim to pass over the upper corner of the ejector. I did not notice that this was happening until about 100 rounds in to testing, and by that point the ejector had been mildly peened in its topmost corner. I tuned the extractor by removing material from the extractor's stop shelf, until it gave enough pressure on the 5.56 case rim so that an inserted case could be spun in the bolt head, but with mild resistance from the extractor claw. This mimicked the behavior of the Saiga .223 bolt. Since then the rifle has been 100% reliable and no further peening to the ejector.  

I lost track of how many rounds I have put through this rifle now but it's probably somewhere in the 500 range. Not a single FTF/FTE or other malfunction, and it recently shot just a hair under 1 MOA at 93 yards with AE 50gr BT.

Here are a couple photos I took of the Beryl mags seated in the rifle. These were taken a while back, they may not show all of the areas that you might want to see. Let me know if you want any additional photos.

mancat thanks so much for the detailed reply.

Tuning the extractor is a good idea. I have not had a problem with it, but what you mentioned would definitely help prevent extraction issues.

I am going to try a Polish Beryl mag and see if there is any improvement.

What you described about the feed lips spreading and letting an extra round pop out of the mag is exactly the behavior I am seeing.  Sometimes I have a round partially chambered, and an extra round stuck between the bolt carrier and trunnion pointed straight up.  I am not sure it's happening for the same reason, but I can say that my mags were VERY right fitting, no slop and no wobble. It's possible that the pressure on the front and rear of the mag when locked in was causing the feed lips to spread as you described during firing cycle.

So I've removed some material from the center support and receiver at the mag catch to let the mags fit a bit loose with some side wobble.  This may resolve the issue.

If not, I'll order a Polish Beryl mag and see how it seats.

Thanks for your help Sir! Nice looking build.,

You will find split opinions on messing with the extractor on these builds. Mine ran fine unmodified,  but as I mentioned I could see some peening on the ejector. The case was loose enough that the ejector was pushing the case rim up towards the extractor on ejection,  causing the case rim to ride over the corner of the ejector a little bit before it was finally ejected from the receiver. Tuning the extractor pushes the rim towards the ejector,  in addition to improving the extractor grip on the rim. This gives much more positive ejection overall due to the elimination of any slop between the case rim,  ejector,  and extractor.

I also noticed that my Saiga. 223 bolt would hang on to an inserted case if you flipped the bolt upside down,  while the unmodified 5.45 bolt would drop the case when flipped. After modifying to get the same level of tension on the rim that the Saiga bolt has,  the bolt no longer will drop the case when flipped. I was worried about the possibility of having an FTE if the rifle was shot at an angle or upside down.



Also what gas port size did you use?  Overgas condition could exacerbate any issues with loose rounds in the magazine.

Ok makes perfect sense thanks.  I don't remember the gas port size.  I did this build a few years ago and just "rediscovered" it in my safe.