I built a 7.62x39 AR and I’m having FTE issues, but only with brass cased ammo. It was initially doing it with steel cased Tula and a new extractor spring solved the issue. I was out shooting today with my son, and we went through a few magazines in it, not one issue with several different steel cases ammo, but put brass cases ammo in it, and every time it’s a FTE. Gas block is not adjustable, but looks fine and buffer spring is standard factory one with a standard carbine buffer. Any ideas to resolve this issue?

Where's it throwing the cases?

I don’t run much steel case but I believe it is quite common for brass cased ammo to stick in the chamber after running a bunch of steel. Clean the chamber and try again with the brass before you shoot steel.

Between the 3 and 4 o’clock position.

This, or just a rough chamber. The brass tends to form to match the roughness more so than steel, and that causes more tendency to stick when a chamber has rough machining marks (or corrosion pits, but that doesn't sound likely if it's new). Good news is that it's a relatively easy fix with a chamber hone in most cases, if you have a gunsmith who knows what he's doing.

If it's a rough chamber, you can see evidence of it on the fired brass if you look carefully at the case body.

Edit - on second thought, please clarify - does the fired case not come all the way out of the chamber, or does the case stay stuck in the bolt and it tries to feed a new round? My comment above is for the first one, but the second one is a different issue that is most likely a bolt or extractor problem.

What weight buffer? Buy or borrow a heavier buffer, I am willing to bet it solves the problem

Who's barrel?

When it shoots brass it’s pretty much a double feed type. So it tries to put a new round in the chamber and the empty case stays in the bolt. The upper is new, and I did not notice issues with the spent brass casings. The mouth of the case has a dent in it, it so does all of the steel casing it shoots just fine.

It has just a standard H buffer in it. It’s what came in the kit I bought

It’s a Kari’s Guns upper. I was going to build a 6.8, but decided to buy something to just play with. Between the lower, build kit and upper. I think I’m $400-$425 into it. The red dot adds another $100 to it. I’m honestly fine just shooting steel case ammo in it, my son on the other hand, thinks dad needs to shoot more expensive ammo through it. That’s what my 6.5 Grendel is for though.

This. A bore snake is your friend.

kwg

I think the problem is a rough chamber or feed ramps at least is the issue issue. I went out again today with a clean chamber, and a heavier buffer. First mag I ran through it was all brass, damn thing was a single shot. One shot and failure to eject, clear it and fire again, same thing. I put in a new mag with all steel casing, not one hiccup. I looked at the brass from the ones I had issues with, and there are rough spots on it. I got home and broke the AR down, and put my pinky on the feed rails, darn near cut my finger it was so rough. I guess I'll brake out the Dremel and give it a nice polish. The only problem, I won't be able to hit the range again for several weeks.

Hudge,

This could be the excuse you need to get a bore scope.
Here' the one I picked up off Amazon, $50.00:

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The first thing I'd try is a lighter buffer.

Sounds to me like the extractor is jumping the rim on the fired case. Look for aggressive extractor marks on the rim of the fired case, to confirm.

If that's the situation, a heavier buffer will retard unlocking/extraction a bit.

I've had that situation with 5.56, and an H3 buffer got it sorted.

If the empty case stays in the bolt it might be under gassed/powered. In other words it sounds like it’s short stroking. Load one round and see if it locks back on an empty mag.

No it was fine with running one in the Mag and then it locking back. It’s only when more than one that is brass cased in the magazine that it acts up.

No worries though, I ordered a new gas tube and gas block for it.

Gas port is the problem.. 1/8 drill bit, drill and open up the gas port. My buddy went round and round with a 450 bushmaster. New gas tube, new gas block, buffers etc. Still didn’t fix it. i talked to Deflave about it short stroking and failure to eject. He said open up the gas port. My buddy did and All problems were fixed and ran like a champ.

.125" is pretty big. I'd start with a #41 (~.096" IIRC) and work up from there.

I agree, start just a bit bigger... if not you go from not extracting to wanting to rip rims off from too much gas.

This.

0.125 sounds about right if you intend to install an adjustable port.

You're getting advice to solve two completely different issues. Overgassing and undergassing can sometimes manifest as the same problem if you don't know exactly what you're looking at. And some of the verbiage used by everyone isn't quite the same.

Can you take a pic of the malfunction, or better a video?

What are the new gas block and gas tube supposed to accomplish?

The new gas tube and block are to get it back up and operational at this point. With the screw being stripped out on the block, I had to drill the stripped screw out to get it off. Once I got enough material remove I was able to "screw" the gas block off, which in turn broke the gas tube. I probably should have just left well enough alone and let it be. After I put the new extractor spring in after the first outing and played with the magazine a little, it fed steel cased ammo with no issues. It's just brass cased ammo it doesn't like.

What mags are you running?

Does the bolt reliably lock open after the last shot of a magazine(when the rifle is operating correctly with steel case)?

Yes, it does. I have not had a problem at all with that aspect when suing steel cased ammo, 50/50 chance it will do it with brass cased ammo. Load 2 or more brass cased rounds, forget it.

ASC mags, I don't think they are the issue, as they have been ran in my son's 7.5" 7.62x39 AR pistol and no issues at all.

Honestly, I think it maybe the darn feed ramps. My son is piecing together a new upper in 7.62x39 with a 16" barrel. He bought a Diamondback barrel, and the feed ramps are like glass compared to the one on mine.

Your son running brass ammo through that pistol as well?

I would try one of these

https://gunmagwarehouse.com/asc-7-62x39-ar-15-30-round-stainless-steel-magazine.html

Holy crap NO! That is absolutely terrible advice. Please don't lead new AR shooters wrong with this kind of garbage.

When you don't know what you're talking about, don't try to "help"; it only confuses the issue and makes everything worse.

There are a lot of guys throwing out ideas. Even the op has some funny thoughts. Now he thinks the feed ramp is the culprit because it isnt nicely polished? How TF does that have anything to do with failure to eject?

and you offered a ton advice to help out the op didn’t you.. I will take advice from Deflave about AR’s before I took any advice from you.

It’s either gas issue or the mags he’s using. The op said it shoots fine with one round, ejects, bolt locks back. But when he puts more than 2 rds in the magazine it’s starts having issues. So I would try a different mag.

He’s running both steel and brass ammo.

While we’re throwing out theories, the dimensions of the loaded rounds may be an issue. If the brass ammo sits slightly higher in the magazine, it may impose drag on the bolt carrier, slowing it just enough to cause problems. This would account for the difference between one round and two in the mag, and the friction difference between steel and brass. Recommend you measure the difference between the two and see if it’s even a factor.

Old70

Lots of pitballing, but here goes another.

old70 has me thinking.

Ever try loading a few steelcases, the a brass?
It would be interesting to see if that made a difference.

The brass case is softer than the steel case. The brass case expands/seals tighter than a steel case.

Upon firing, the pressure/heat expands the brass case tighter against the chamber forming a great seal. Steel case essentially does the same, but not to the same degree.

As pressure/temp drops, the seal breaks, facilitating extraction.

If the bolt is trying to unlock/extract before the brass case has 'broken seal' the extractor hook can jump the rim, leaving the fired case in or partially in the chamber.

The bolt continues rearward, picks up the next round from the magazine, and pushes it forward toward the chamber, except the chamber is not empty.

Classic double-feed type of jam.

An adjustable gas block is one way of addressing the situation, by dialing down the volume of gas.. A heavy buffer will usually work too, as it retards unlocking/extraction.

I've been through this with one of my 5.56. An H3 buffer sorted it out nicely. Now I'm running (yes I said 'running'...lol) H3 buffers in all my carbine lowers, and everything runs well. I'd probably need the standard buffer in the arctic.

I'm no expert, but I believe that this is what's happening. Especially since the OP indicates that lockback is happening with a single round.

Hudge said, "I think the problem is a rough chamber or feed ramps at least is the issue issue. I went out again today with a clean chamber, and a heavier buffer. First mag I ran through it was all brass, damn thing was a single shot. One shot and failure to eject, clear it and fire again, same thing. I put in a new mag with all steel casing, not one hiccup. I looked at the brass from the ones I had issues with, and there are rough spots on it. I got home and broke the AR down, and put my pinky on the feed rails, darn near cut my finger it was so rough. I guess I'll brake out the Dremel and give it a nice polish. The only problem, I won't be able to hit the range again for several weeks."

Everything I read says the empty case stays in the bolt, does not eject. And it only locks back 50/50

There is no way to diagnose this with the given info but everyone is throwing something out there.

Is your ejector and spring good? Doesn't matter what it does with steel, brass is the problem you're having. It could be a mag catch out of spec or weak ammo.

I must have misunderstood. I thought the spent case was staying in the chamber, or partially extracted but not ejected.

Some company and I don't know who they were/are was putting out some 450 Bushmasters that refused to extract and eject. My local gun guy did everything he could to get the problem guns (plural) to work. His last effort to get them to function was to open up the gas port. That fixed the problem. They were simply under gassed.

However, he used the number drills and picked out a number slightly bigger than the existing hole. If that did not work he went the next number up. He didn't just pick out a drill bit he thought was OK and use it. A 1/8th drill bit is .125" diameter hole. I think his final number was in the .090 range. .125 is probably going to over gas the rifle. Find someone with the numbered bits and work up from the existing hole until the gun is reliable.
kwg

If you have another (working) AR it should be simple to isolate the problem.

You are correct. My new gas block and tube will be here today, and I will get it back together and go one by one on the things mentioned to get it fixed.

"So it tries to put a new round in the chamber and the empty case stays in the bolt."
"One shot and failure to eject, clear it and fire again, same thing."

I just read what you wrote and tried to grasp how the empty case could stay in the bolt but it's what you wrote. In the future please note failures to eject are different than failures to extract.

I hope you get it sorted out.

Once you get the gas block off, stick the shanks of number drills in the gas port. Let us know what the size is of the largest drill bit that fits.

Based on what he's said, that steel case ammo functions but brass cased ammo does not, it doesn't really sound like a gas pressure / volume issue.

If there's enough gas to extract & eject the steel case, it would seem likely to be enough gas for the brass case ammo, absent some other contributing factor like the rough chamber...............maybe.

Really hard to get an answer from the crystal ball w/o see the gun.

If you ever get it figured out, report back with results.

MM

If the bolt won't let the brass case go, maybe check the ejector plunger/spring for crud.

also maybe compare rim diameter between the steel and brass cases. If the brass ammo has oversized rim diameter, that might be an issue depending on boltface diameter.

Yes, this. Small changes in gas port size, like going from .086" to .093", can have a big effect on how the rifle runs. One would have to be completely oblivious to this stuff to suggest drilling out to .125" without a lot more info and testing smaller port sizes first.

I go from .093" to .096" on a lot of my rifles and notice a large increase in reliability.

If that 1/4 bit don’t work move up to a 5/32 that should get that AR running for sure..

That would be a 3/32 correct?

.0937" = 3/32

MM

I use number drills. #40 is .0935" and #41 is .096"

20" barrels with rifle gas?

I thought that was settled long ago, haven't heard of any reliability problems with a 20" rifle.

Where did you get them from? Be handy to have a set. Thanks

The fact that you have to ask says a lot about whether you should be giving advice on opening up gas ports. Stick to what you know, instead of believing other blowhards and claiming it as fact.

Any good machine tool supply sells number drills, which you'd know if you had any experience with this sort of thing.

Yes.

Service Rifles are a different beast. They have really heavy barrels and parts, like gastubes, tend to get over-recycled.

IMO&E .093" 20" heavy barreled rifles don't have a particular affinity for powders like WC844, 845, SMP-842, 8208 and sometimes AR Comp & similar. A significant number of rifles simply won't run with those powders at that port size. If I were to speculate, I'd say it has to do with gas keys that were assembled without a sealant, but I'm not sure even that is necessarily 100%. .096" runs with any reasonable carrier and is what Frank White uses.

The heavier the barrel, the bigger the gas port needs to be.

I inherited the number drills, but I'll bet Harbor freight stocks them. You need to run them well lubed at high speed when using them to ream stainless.

Harbor freight sells them as well.

you want the bullet going out the muzzle , not the gas port!!

I prefer to use good drill bits, not Hobo Freight junk, and wouldn't dare put a HF drill bit in a good barrel. You want to avoid creating a burr on the inside, and starting with a good sharp drill bit that cuts well is pretty important.

Most of their equipment of this nature is only adequate for woodworking anyway. It's getting hard to find good gear on Amazon too, unless you really know what brand you're looking for; there is so much low quality chinese junk being pushed there that it's hard to find the good stuff sometimes.

High quality drill bits are not very expensive, and are easily available from reputable places. McMaster, Fastenal, and Brownells are my main choices, MSC and Grainger if I have to.
I do a lot of metal machining and have learned a long time ago to not waste money on junk drill bits.

Edit - figured I should clarify the recommendations here: there are a bunch of good brands of drill bits, so it's not worth listing them all. Easy choice is to order them from McMaster Carr; they don't sell junk and if you order the right bit for the job, it'll do what you need. A 135° split point HSS stub drill is what I prefer, don't want carbide for this. A tip to reduce the amount of burr in the hole is to drill a couple number sizes smaller first, then finish with the correct size only removing about 5-6 thousandths. Also, for drilling gas port holes I only use the final size drill once or twice, then set it aside for other jobs. This has given good results for me in a bunch of SS and CM barrels.

Also, if you're using a drill press instead of a mill, put a cleaning rod in the barrel before drilling, it'll stop the drill from touching the far side of the barrel.

Remember to back the port up with a lead slug if you drill it.

Thanks Yondering.

Good stuff.

I just went out and measured, no drilling with a normal standard drill bit and a 3/32” fit in the gas port just fine.

Pardon if I missed it, but what length is the barrel? What gas length?

On a 20" you could stand going up to a #41 or even 42, maybe 43.

A 7.62x39 is going to need little bigger port than a 5.56. My references say a .078" port with carbine buffer is going to run a mid gas 16" 5.56. If that's the case, I'm guessing 3/32" is probably going to be a little too large.

Tyrone,

It’s a 16” barrel with carbine length gas tube.

I compared the rim diameter between the steel case I have on hand and two different brass ones, all three are identical in size.

Colt 6920's have a .062" gas port.

Perhaps someone here with a similar barrel that runs well could share their port size.

I have no idea what size port a 7.62x39 would run but we need to know if he's having a failure to eject or failure to extract problem before we can offer ideas in the right direction.

But I have a feeling he's just screwing around.

No, I'm not screwing around, I'm waiting on a barrel nut to come in so I can properly put the barrel back on. I got my new gas block and tube last week, I just need to find the time to get everything back together and go to the range to see how it shoots. If the issue still exists, I will take pictures and post them.

Keep us posted Hudge.
I really like the idea of uppers in that caliber.

It doesn't work to compare gas ports for different cartridges and expect them to match. You're talking about a 5.56 barrel, he has a 7.62x39.

I don't know why everybody's talking about drilling gas ports anyway; nothing in Hudge's comments indicates the rifle is undergassed.

Hudge, I asked in post #5 in this thread about the type of failure, and you answered in post #8 that it tries to feed a new round while the fired case stays in the bolt. That's a bolt problem, not a barrel problem. You've got issues with either the bolt itself, the extractor, or the ejector. The easy button is to try a new complete bolt, if you don't know what issues you're looking for in the bolt you have. It may be something simple though like a piece of debris jamming the ejector pin.

A dirty or rough chamber may also be an issue combined with brass forming against that better than steel, as we already discussed.

Until you address those issues or provide more info, you'll just continue to get a lot of guessing, and most of it is pretty misleading to be honest.

And then he says this claiming an extraction problem and the somewhere else he says when loading one round at a time it locks back on an empty mag about half the time.

That's why I thought you were just screwing around with us, cause you've described 3 different failures.

Exactly.
But it does provide a frame of reference. The .30's need larger ports than the .223s. However, given Hudge's .094" gas port, I think he has a problem with the gun being grossly over gassed as well. It's gotta be bigger than the Colt port, but I doubt that much bigger.

I do agree with you that it is an extraction problem with the bolt, but being perhaps grossly overgassed sure as hell doesn't help. A gun can be so overgassed as to rip off rims.

Sorry I wasn't clear on that, I don't like to speak in absolutes when I don't have experience with the exact problem presented. I much prefer to lay out breadcrumbs and let the person with the problem work their way through it.

What needs to happen:
Put the broken rifle back together.
Take video of the malfunctions, including close up shots of the malfunction. Preferably close up slow-mo video of the action.
Everybody shut up and stop "helping" until that happens.

People are talking about what drill bits to use to waller out the poor guy's gas port, based on what size port a 20" .223 uses, when there's likely a 0% chance the home built gun's barrel, assembled by a guy who doesn't know what the parts of the gun are called, purchased to feed steel case ammo, has a gas port that's too small.

Yep, 8 pages of wasted time...................started by someone w/o a clue.

MM

Here is the video you requested

Good luck with it. I hope you get it figured out.

Thanks for all that said it was an extractor problem. I ended up replacing the bolt, not the whole BCG, just the bolt and it runs like a charm.