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7.62x39 AR Issue

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Hey all, I recently put together a 7.62x39 AR-15 and I'm have extraction/cycling issues with it. The rifle has a 20 inch barrel with rifle length gas port with an Adams Arms piston system and BCG. The gun fires fine, but is not cycling. I initially thought I might have a misaligned gas port/block, but recently took note of the fact that manually cycling the spent case is overly difficult. I actually have to give the charging handle a good solid pop to extract. The gas piston is moving freely so that isn't the part that is binding. The BCG moves freely and does not stick when cycling on an empty chamber or when cycling live rounds through without firing them. The sticking only occurs upon firing the round. I can see no obvious deformations or damage to the fired casings. The bolt moves freely within the carrier and the spring returns the bolt to proper extension after pressing the bolt into the carrier. Any clues as to what I'm running into here?
 
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Spent case is hard to extract, but not live round. Sounds like a chamber issue. Are you using lacquered steel case ammo?

Sticky chamber and under gassed?
 
OP
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Spent case is hard to extract, but not live round. Sounds like a chamber issue. Are you using lacquered steel case ammo?

Sticky chamber and under gassed?
Ya, it's TulAmmo. Can't recall if its lacquer or polymer coated. I was thinking along those lines and was going to run some brass cased stuff through to see what happens. Are there any solutions to get the steel case stuff to cycle better? Gotta save those pennies.

Also, this gun has been a back burner project which I had completed and taken out on its maiden voyage last summer. Back then, I had intermittent firing, which has been corrected with the modified firing pin, but I seem to remember it cycling properly when it did fire, IIRC.
 
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If it were me, I’d find some fine diamond lapping compound and clean up the chamber. You could use a larger size barrel mop attached to a drill motor and polish it up.

Maybe something like this

BC5A9223-1F46-4C95-A7D6-CAFC1EB415DC.jpeg
 
OP
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If it were me, I’d find some fine diamond lapping compound and clean up the chamber. You could use a larger size barrel mop attached to a drill motor and polish it up.

Maybe something like this

View attachment 585246
Interesting. I'll be picking up some brass-cased ammo today but I'll also give the lapping compounds a look too. Thanks for the recommendation.
 

Reno

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Having trouble shot a ton of AR15s. I find a majority of them are built perfectly fine. The mixed match components usually tend to have cycling issues. Those issues tend to be derived from short stroking. That’s usually caused by underpowered ammo. If the ammo you want to run is underpowered, the gun is undergassed or over buffered or a mix matched component don’t like one of the mix matched components. It could also be as simple as adding a bit more lubricant.

Cycling issues on home brew AR15s are common. I swear I’m not surprised a good checklist doesn’t exist to help solve them.
 
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Having trouble shot a ton of AR15s. I find a majority of them are built perfectly fine. The mixed match components usually tend to have cycling issues. Those issues tend to be derived from short stroking. That’s usually caused by underpowered ammo. If the ammo you want to run is underpowered, the gun is undergassed or over buffered or a mix matched component don’t like one of the mix matched components. It could also be as simple as adding a bit more lubricant.

Cycling issues on home brew AR15s are common. I swear I’m not surprised a good checklist doesn’t exist to help solve them.
Hey Reno, that was me and my buddy you met out there when you were hanging signs on Wolf Creek. Nice jawin' with ya and thanks for sharing your toys with us.
The issue with this rifle definitely isn't short stroking. The BCG isn't moving at all upon firing at this point due to the significant force needed to get the case out of the chamber. I think 308's post is leading down the right path. It's either the steel/lacquered case and/or I've got a bit of roughness in the chamber that the expanded case is grabbing onto. I'm digging around looking for chamber lapping/polishing procedures at this point, and I'm going to run some brass cased ammo through it to see what effect that has.
 

Reno

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Hey Reno, that was me and my buddy you met out there when you were hanging signs on Wolf Creek. Nice jawin' with ya and thanks for sharing your toys with us.
The issue with this rifle definitely isn't short stroking. The BCG isn't moving at all upon firing at this point due to the significant force needed to get the case out of the chamber. I think 308's post is leading down the right path. It's either the steel/lacquered case and/or I've got a bit of roughness in the chamber that the expanded case is grabbing onto. I'm digging around looking for chamber lapping/polishing procedures at this point, and I'm going to run some brass cased ammo through it to see what effect that has.
It was nice chatting you two up.

Ya, AR symptoms are never fun to have to figure out! It’s always better when they go together and work the first time!

I’d give the chamber a darn good cleaning with a bore brush chocked up in a drill. That should get it good and clean. Then run the brass stuff. Then if it’s still a tight chamber, start lapping compounds.

I never recommend any sort of permanent modifications until all other trouble shooting has been performed.
 
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Tula is polymer coated ammo, after complaints of lacquer "melting."

Lacquer coated ammo has been running fine for decades, and never became an "issue" until people ran it in their 5.56 ARs (at which point the issue was steel case is just dirty and shooting brass after is a bad idea).
 
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Tula is polymer coated ammo, after complaints of lacquer "melting."

Lacquer coated ammo has been running fine for decades, and never became an "issue" until people ran it in their 5.56 ARs (at which point the issue was steel case is just dirty and shooting brass after is a bad idea).
I kinda get your point, but I really don't think this is a case of a dirty chamber. See attached photos, which shows the chamber and bolt without any cleaning after last range session, about 10-15 rounds. The gun has only had about 40-50 rounds total through it. I built it and took it out last summer, had intermittent firing which was due to using a 5.56 firing pin and hammer spring.(It is a 7.62x39 bolt.) I put one thirty round mag through before getting tired of the misfires, acknowledging it was unworkable at the range, and putting it back in its case. I did my research, replaced both the spring and firing pin, and the gun was cleaned before going back into the safe. Upon taking it out a few weeks later, the gun would fire on every round, but would not cycle. It behaved like this on the first round and every round thereafter. It didn't get progressively worse. The BCG failed to move at all on the first round, on a clean chamber, and has not cycled on its own since. Again, the BCG cycles fine on an empty chamber, and will cycle live rounds in and out of the chamber, no problem. As soon as you fire a round, the BCG/casing seizes up and you have to cycle manually.
IMG_0722.JPG
IMG_0724.JPG
IMG_0727.JPG
IMG_0740.JPG
 

Reno

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Could be horrible carrier tilt.
 
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Kept shooting it, but it didn't happen as much to begin with.
This is why I thought the lapping/polishing may be a decent idea. Take a few millionths of an inch off the chamber to open it up a RCH and smooth things out to reduce excess friction. Also why I thought brass cased ammo would be better as brass already has better lubricity than steel.
 
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Could be horrible carrier tilt.
It is a brand new YHM receiver and brand new AA BCG, but that doesn't necessarily rule that out. I don't see any obvious differences when comparing to my other piston BCGs. Any measurements or tests I could perform to rule that out?
 

Reno

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It is a brand new YHM receiver and brand new AA BCG, but that doesn't necessarily rule that out. I don't see any obvious differences when comparing to my other piston BCGs. Any measurements or tests I could perform to rule that out?
Not really. Just check the buffer tube. If it’s got funky stuff going on could be tilting really badly.

After hearing you talk about it more, I’m still thinking it’s short stroking and not a stocky chamber. Especially if there isn’t any issues manually cycling the action.

That or it’s something as simple as the piston not in the right setting or perhaps assembled incorrectly. If the bolt carrier doesn’t even move when fired, perhaps looking at the piston and checking it for abnormal conditions. If the gas block is set to off, that would be a super easy fix.
 
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Not really. Just check the buffer tube. If it’s got funky stuff going on could be tilting really badly.
OK, pulled the buffer and spring, inspected, no signs of abnormality. Buffer moves smoothly within buffer tube. Its an H1 buffer so shouldn't be a contributor.
After hearing you talk about it more, I’m still thinking it’s short stroking and not a stocky chamber. Especially if there isn’t any issues manually cycling the action.
Definitely not short stroking. It isn't even coming out of battery upon firing. Firing a round results in a flat "clunk", and the BCG does not move. It does have issues cycling manually. After firing a round, pulling on the charging handle, it is possible to extract the case, but it requires a significant amount of force, as if something is stuck, but it will come free and extract/eject. Following live rounds will chamber and extract as long as they are not fired. Take the mag out and the BCG cycles fine. Put another live round in and pull the trigger, "BAM/CLUNK", no BCG movement. Manually extract with force.
That or it’s something as simple as the piston not in the right setting or perhaps assembled incorrectly. If the bolt carrier doesn’t even move when fired, perhaps looking at the piston and checking it for abnormal conditions. If the gas block is set to off, that would be a super easy fix.
This was my first suspect. I moved the gas block through all of its settings with no change in performance. I locked the bolt back and could then push on the piston, which moves freely. I had tried moving the gas block up and down the barrel a mm or so, thinking the port wasn't aligned, but this also yielded no change. This latest shooting session was when I finally took note of the difficulty of manually extracting the spent casing.

I seriously appreciate you guys thinking this thing through with me.
 

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