Hello,

Built a 7.62x39 variant and initally had issues with it short stroking (fired 5 rounds), it would extract and eject but didnt pick up the next round or lock back on empty. I noticed no issues hand cycling prior. Bolt and barrel are faxon.

I got lighter spring / buffer (gas block/tube is pinned in position)

I went to hand cycle it and bolt was stuck with round in chamber. Mortared it, checked it, tried again same result. Sometimes it would fail to extract during these troubleshoot sessions, leaving round in chamber, which would freely fall out when gravity was applied.

I also noticed the bolt needs more force forward than normal to seat properly with the round in the chamber, maybe that's normal with 7.62x39 AR?

CMP sprayed the hell out of it, cleaned it, and it hand cycled 2 rounds before mortar every round.

Checked bolt and chamber and it appears no flakes or obstruction, barrel is clear.

Ammunition is red army steel cased. I don't have any brass 7.62 around.

Any more ideas?

Any other 7.62x39mm chambers handy?  Any Go/No Go gauges?

Nope, but that was my next thought as well

Surely you have a neighbor w/ an SKS or AK.

Pics of the round in the bbl, no bolt?  Do the rounds slip in & out easily by hand?  Will the round fall out when you tilt the bbl to the rear?

Oh duh, I have a AK and SKS. I'll verify but the round would fall out freely when it failed to extract the one time it did.

When I get home I'll mess around more and take pics.

Rounds can be inserted and removed freely from barrel. Gravity has them fall out.

Here are some pics

https://ibb.co/s3QxtdV

https://ibb.co/z4fcbPR

The 7 62x39 bolt has a hard time locking into the chamber with a round in it. 5.56 I can do it relatively easy with a small tap on the bolt. 7.62 I can't do it by hand at all.


I'm beginning to think headspace or something is majorly off.

Edit: So I've manipulated it a lot. It will mortar every 10th, 15th round now. The rounds are sometimes failing to feed from the magazine / getting caught in feed ramps (m4 style properly aligned). The bolt fails to extract 1 out of 4 rounds now, leaving the round in the chamber. Round freely falls on it's own.

I've noticed the locking lugs are unlocked and beginning to move out of the chamber but stop when aligned with the chamber lugs, making me think the bullet is pressed / stuck inside when I have to mortar it.

The more I mess with it, the more random it gets. Between mortaring 15 in a row to hand cycling 15 in a row to hand cycling but failing to extract 5 in a row to failing to feed the next round. What a mess this is

I'm thinking you want a set of Go/NoGo gauges.  Or take it to a gunsmith that has a set.  Are you able to measure how far the round goes into the chamber vs how far it goes into the chamber on your AK or SKS?  What does the spent brass look like?

When I shot it the few times I did, there were no marks that I saw on the casings.

Now there's marks quite all over the casings. Even took a chunk out of the bullet at one point. Like I said, it's a mess. I think it'll be going to a smith for a second opinion.

Attached File

Built a 7.62x39 variant and initally had issues with it short stroking (fired 5 rounds), it would extract and eject but didnt pick up the next round or lock back on empty. I noticed no issues hand cycling prior. Bolt and barrel are faxon.

I got lighter spring / buffer (gas block/tube is pinned in position)

I went to hand cycle it and bolt was stuck with round in chamber. Mortared it, checked it, tried again same result. Sometimes it would fail to extract during these troubleshoot sessions, leaving round in chamber, which would freely fall out when gravity was applied.

I also noticed the bolt needs more force forward than normal to seat properly with the round in the chamber, maybe that's normal with 7.62x39 AR?

No, it is NOT.  

check your gas tube alignment to the bolt carrier.  

It sounds like it may be off.

If off at the gas port - it might restrict gas flow needed to properly cycle to system.

ALSO - & I think this may be your problem. sometimes if the barrel & nut is not property aligned - the gas tube end in the receiver may be at an angle / not be concentric (it might interfere with / make contact with) the BCG Gas key.

Also what Magazines are you using?

Bigger_Hammer

If the tube was off, the bolt would bind and stick without a round in the chamber, correct? It only shows these issues when a round is involved.

I actually did check the alignment and it appears good.

C products duramag, 10 round and either the 28 or 30 round. Both brand new, minus the use I've done.

Good Magazines.

Gas Tube doesn't appear to be an issue.

Just a shot in the dark, but have you disassembled the 7.62x39 BOLT to check the extractor (it would sit further OUT when a cartridge was in the bolt face) - thus it might cause binding WITH a cartridge, but not on an empty bolt.

Bigger_Hammer

My suspicion the whole time is a bad extractor. But I'm not entirely sure how to tell that it is "bad".

I can say that the rim of the cartridges were becoming "sharp" when they were being extracted. I also had a very small filing of steel come off the lip of the cartridge from the extractor grabbing it.

Likely not your big problem, but I blended and enlarged the feed ramps of the upper and barrel while assembled on an 11" 7.62x39 AR pistol.  I was able to get consistent round feeding after that.  I do think that the 7.62x39 bullet can and does catch up on M4 feed ramps.

The two main problems encountered with 7.62x39 in an AR is 'Tip drop' and over gassing. The over gassing is resolved by a heavier or reciprocating buffer, tip drop is corrected by appropriate mags with a highly pronounced bend. The extractor marks on the case rim are indications of over gassing, there is no need for feed ramps if the correct mags are used.

None of the rounds in my troubleshooting are fired. All are hand cycled regarding the issues I've described. The gun was actually under gassed even with a standard spring and buffer. Gas block alignment checked and rechecked (its also pinned).

Chamber was polished and gas port drilled one size bigger. It doesn't short stroke anymore when firing however still cannot hand cycle rounds reliably without having a mortar needing to occur.

The rounds in question are red army standard tulammo steel case that have ran great in my sks and AK hunter rifles.

I'm going to try different brands of ammo along with some brass case to see if it changes the result. The gun also headspaced properly.

My only other idea is trying a different bolt.

Also, the two duramags I have have run mostly well. There were a few fail to feed where the round hung up prior to leaving the magazine. Both a 10 round duramag and 28 (or maybe it's a 30) duramag did it. Haven't cycled enough after the polish to comment if that may have improved it. But just my experience and always YMMV.

Update:

Tulammo (steel), Wolf (steel), Winchester (brass) all presented the same issues. The bolt would unlock upon trying to extract/eject but seized. I had to mortar 1 out of every 2 rounds regardless of steel or brass. Loaded in both duramags, same issues at same failure rate.

I had continuous fail to feed from magazine issues with brass (Maybe cause soft point vs FMJ). Still common with the steel cased FMJs though.

Chamber has been polished. I've tore down everything it seems at least once to check things over without locating any issues.

To put it blatantly, I may break it all down and sell it. For the issues I've had, I should've just got myself an AK.

the barrel-extension feed-ramp overhang is not ideal, and could explain why a chunk was taken out of a bullet.  but that would not have anything to do with why you're having to mortar.  unless the slight misalignment of the feed-ramps indicate that the barrel extension not being clocked 100.0% is keeping the bolt from being unlocked, but that would have to be a very finicky BCG (on the edge of specs for clocking angles) for that to happen, I've seen more feed-ramp misalignment and not affecting bolt unlocking.  could be tolerance stacking.

but that feed-ramp overhang is definitely bad news, but unrelated to needing to mortar.

I've built over ten 7.62x39 AR-15 uppers, and they all work fine, various configs, and not had the problems you're observing, especially since you said the headspace checks out good, verified with HS gauges.

on all my 7.62x39 builds, i do deburr and take off the sharp edges of the feed ramps IAW Hellbender's guide, make sure there's no feed ramp overhang, check headspace with gauges.  I've got a couple of builds with Faxon barrels, and for most, if not all of my builds, I've been using Aim Surplus BCGs.

I also hit the mag feed lips with a stone file to knock off the as-stamped sharp edge which tends to carve out gouges on the case, who cares about that since you're not reloading the steel-case ammo, but sometimes it prevents the round from tilting up the feed ramp, not being released (bolt over-ride).  Again, not related to mortaring.

if your headspace checks out ok, and the bolt is not unlocking, might be something with the cam slot of the BCG being slightly off, or the radial angles (clocking) of the bolt lugs being slightly off, so that when the bolt carrier comes all the way back. and tries to pull the bolt out of the barrel extension, the lugs are still just slightly engaged, overlapping, preventing unlocking.  If so, then I suspect the mortaring is not to unstuck a stuck cartridge, but rather to jar the bolt head to get it to unlock, to jiggle the bolt to get the lugs to dis-engage.  You might see evidence of that on the back-side of the bolt lugs.

sorry, that's all that comes to mind.

Now that's a great observation, and a great hypothesis to what may be occurring. The weird thing is, the bolt does unlock and seems to initially clear the chamber before getting stuck. I will inspect my bolt a little more thoroughly.

I decided to contact Faxon and ask if they're able to assist in any way. I believe it's not an installation issue, rather, a tolerance or manufacturing issue.

my guess is you're observing the bolt head rotating to unlock, and perhaps just the bolt carrier coming rearwards.  Is the bolt head itself actually moving rearward when it's getting stuck?  I suspect not, just the bolt carrier moving rearward.

Pretty sure the bolt is moving too. I've honestly given up on trying to figure it out at this point and shot an email to Faxon.

We will see what they say or offer for any service, if any is available for me in my particular issue.

Faxon replaced the BCG after I explained the issue. Issue resolved. I noticed the bcg has a different model / item number on it. Possibly an improved or different version.

Hand cycles and fires great now.

Great!  thanks for the follow-up.

Steel case, is junk. It won't be long before you won't be able to buy it at all. Russia always implodes when it comes to markets.

Buy a 7.62x39mm bronze bristle chamber brush and keep that chamber clean. A flexible handle cleaning rod is what you need.

I had to open the gas port on my 20" rifle gassed (DPMS barrel) 7.62x39mm barrel in order to get it to cycle. I ended up with a .125" (1/8") gas port. AK-47's have huge gas ports. The case (small) and powders used (fast burning) do not create a lot of port pressure. If you look at reloading powders for 7.62x39mm the slowest usually listed is H322. The powder charges aren't much heavier than .223. When you figure in bore diameter, port pressure and gas volume is pretty low.

I built one that had mysterious binding.
Itt was the gas tube hole in the upper pushing the gas tube out of alignment, causing binding.
Filed it to fit and it has run fine ever since.

I feel you bud. Use your ak or sks for home defense.  This stuff is really frustrating Why can't they build it right the first time...