My first AR: 7.62x39 with Superlative Piston kit - Learning from failure...

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10-29-20, 22:06
Bret

Quote:

Originally Posted by turnburglar

2. The AR magwell will not accept a magazine designed for the larger diameter round. Good luck finding anything close to a reliable magazine that holds a decent amount of rounds. My buddy tried a 7.62x39 AR; and mags were the biggest blocker.

This is (no longer) correct. Years ago, 7.62x39 AR15 magazines were not reliable. Now there are options that are. I have RZE Unimags, ASC and D&H magazines. The ASC and D&H are designed specifically for 7.62x39. The RZE Unimags run multiple cartridges. All run 100% in a my Windham Weaponry and Bear Creek Arsenal AR15's. I even put those uppers on my M16 lower and they run through the 7.62x39 on full auto without issue.
https://www.youtube.com/watch?v=ma82EphaORQ&t=1s
10-29-20, 23:56
Pressingonward

A bit of an update - I measured the gas port in the piston gas block and it is also 0.125" - same as my barrel. I was wrong when I said it looked smaller.

Looks like option #1 is off the table. I'm open to options #2 or #3, leaning towards selling/trading the Superlative Arms piston kit and replacing it with a standard gas system, but if I find a good quality barrel with a carbine length gas system I might go that route still...

I can't post on the EE forum yet, but if anyone has an interest in my barrel or piston kit send me a PM.

Again I want to thank everyone for your advise so far, it's appreciated!
11-02-20, 18:58
cspackler

1st of all, much respect for attempting an off-caliber build and piston on top of it.
I don't know much about dez arms but mid gas is fine on x39 so it would be fine if you want to try DI. I wish my 16" carbine were mid but it works so I'm leaving it. I use a rifle buffer with tubbs 308 flat spring.
A regular block, tube, and bcg should be much less than the piston. Maybe just hold onto it for a later 5.56 build.
Cpd mags (duramag) are gtg and I haven't suffered a single failure in over 2k rounds between 7.62x39 and 6.5x39.
11-02-20, 23:34
Pressingonward

Thanks for the input. On a bit of a hold right now until my new debit card shows up...someone a few states over ordered $20 of Taco Bell through Doordash with my old card somehow. My bank takes care of it, but it's sure inconvenient...I think this is about the 4th time I've had a card number get stolen.
11-07-20, 21:48
rpoL98

i had a similar experience, but with a mid-gas 14.5" 7.62x39 Faxon barrel. with an Adams Arms piston kit. I forget what the diameter of the short vertical channel is on the AA pic-rail gas block that mates the gas regulator plug with the barrel gas port, I think it was .1570".

the 14.5" mid-gas 7.62x39 barrel will be more worse than your 18" case. I ended up drilling the gas port in the barrel to .1520", #24 drill. that is Yuuuge, I know, but that's what it took. The AA GB that I was using has the removable gas plug. Ended up drilling that out from 1/8" to 9/64" (.1406"), required a carbide bit. the 9/64" gas plug hole does make a difference between cycling successfully, and short-stroking.

on the barrel gas port, .1520", I did use a small round file to deburr the forward edge of the hole to minimize shaving off copper jacketing from the projectile, that seems to have worked, not a lot of copper residue in the piston area.

Your 18" mid-gas situation should hopefully be easier to resolve than my 14.5" mid-gas, since you have a whole helluvalot more dwell time before the bullet leaves the barrel.

My 14.5" mid-gas piston 7.62x39 is indeed a nice shooter. nothing but Wolf steel case ammo, that's what I built it for.

Good Luck!

https://i.imgur.com/6Tq9AI7.jpg

https://i.imgur.com/00Pl0B2.jpg
11-07-20, 23:22
Pressingonward

Wow, thanks for the info!

Glad you were able to get yours running reliably.

I broke down and bought a Rubber City Armory BCG and a YHM gas block to convert it over to DI. I think it'll be a more reliable solution and I want to have a solid working rifle given the current state of our nation. I think I could have got there with the piston kit, but I'll save it for the next build. Hoping the BCG and gas block show up this week so I can try it out. Also ordered a Daniel Defense front sight.
11-08-20, 06:58
Bret

Not 7.62x39, but I built a midlength 6.5 Grendel upper that uses an Adams Arms piston kit. What I found is that there's a small window for reliable function. If I use a carbine buffer, it runs in semi, but I get carrier bounce in full auto. If I use an H2 buffer, it sometimes short strokes. If I run an H1 buffer, it runs in semi and full auto. I do wonder if extreme changes in temperature would impact the results.
11-12-20, 20:03
NQNPIII

I have 3 mid gas X39's. 2 16" PSA's, and a 10.5" Alpha Sports.

ASC Mags suck. I have a bunch still in the unopened pouches if someone wants to buy them. I have heard good and bad on D&H. I don't have any. I don't have any Duramags. I do have C-Products Defense mags. All 30rd, they have run 100%. I run heavy buffers. They will run with a 3.0 standard carbine buffer. So far I have ran up to 6.1oz.
11-12-20, 20:06
NQNPIII

Quote:

Originally Posted by Bret

This is (no longer) correct. Years ago, 7.62x39 AR15 magazines were not reliable. Now there are options that are. I have RZE Unimags, ASC and D&H magazines. The ASC and D&H are designed specifically for 7.62x39.

Would you say the C-Products are specifically designed for the x39? I would.
11-12-20, 20:52
rpoL98

Quote:

Originally Posted by NQNPIII

I have 3 mid gas X39's. 2 16" PSA's, and a 10.5" Alpha Sports.

ASC Mags suck. I have a bunch still in the unopened pouches if someone wants to buy them. I have heard good and bad on D&H. I don't have any. I don't have any Duramags. I do have C-Products Defense mags. All 30rd, they have run 100%. I run heavy buffers. They will run with a 3.0 standard carbine buffer. So far I have ran up to 6.1oz.

I have both CPD and ASC mags. both are reliable. admittedly, my ASC mags are well worn-in, and all the edges are smoothed out, so that the round strips out of the mag and up the feed ramp reliably, effortlessly. I didn't grind down the front edge, that's a pointless old-wives tale.

I think key is smoothed feed ramps that don't gouge the cartridge case, bullet tip, and and also smoothed mag feed lips so that the cartridge can pop up, out of the mag as the bullet tip on the feed ramp tips the cartridge upwards towards the chamber. Newly manufactured mags, still have a sharp edge on the mag feed lips, that gouge into the cartridge case, and prevent it from tipping upwards.

that's been what i've found. YMMV.

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