View Full Version : Piston AR in 7.62x39 - build/range report

June 18, 2017, 17:52
As I am away from home, tho' not far, I finished an AR 47 build the during the week's evenings, having done the barreling at home prior, and not in my Savannah apartment. Anyway, last weekend I took it to the local quikshot 25 yard indoor range and test fired it, and 'roughed in' the UTG 3x9 $99 scope. So being a 'Gorper', I went to the Richmond Hill DNR range today.
Largely pleased, just a few issues - I have the stronger hammer spring in there, and the extended 7.62 firing pin, carbine buffer and spring, and the barrel extension feed ramp modified, the 6pm position one as per the Bushmaster example.
Some issues with rounds not going off, failures to feed and some slight dimpling on the primers - I would say 3% failure to go bang rate, with a 6% failure to feed. I was using 122 Tula and 154 Tula, in 20 round Asc mags, and 30 round C prod mags. The 20 rounders were the most dodgey, one mag in particular would not take 20 rounds, 17 is all it would take. The 30 round C prod mags were fine with the 122 Tula, and fed the 154 grains stuff better than the 20's, though neither were perfect.
I wasn't being too particular, certainly not taking notes - just happy to be out doing stuff for myself.
Thinking I may need a heavier buffer!?!?!?!?!

Yeah I know the floor is dirty, and there's no mag or liquor!:)

http://i1064.photobucket.com/albums/u370/Tripcyl/fullsizeoutput_947_zpsujuhjphh.jpeg (http://s1064.photobucket.com/user/Tripcyl/media/fullsizeoutput_947_zpsujuhjphh.jpeg.html)

The top target is the 122 gr Tula, the lower the 154 gr Tula at 100yards

http://i1064.photobucket.com/albums/u370/Tripcyl/385912c6-e9ea-4720-8a77-aae05d0669b9_zpszpginnpf.jpg (http://s1064.photobucket.com/user/Tripcyl/media/385912c6-e9ea-4720-8a77-aae05d0669b9_zpszpginnpf.jpg.html)

Still I had lots of fun - the Range officers were great down there, very interested in the rifle - and saw my logic in 20 cents and less in round cost. This is my 2nd Piston AR build in 7.62x39, this one uses a $89 melonited barrel from Deltateam tactical, the first I used the more expensive Omega barrel, the melonited cheaper one appears more accurate - certainly was harder to drill tout the gashole. My first build has similar issues with soft primer strikes, though with only the extended firing pin, no Wolfe spring - both barrels have the gasohole reamed to 1/8th inch, with an Adams arms piston assembly. Anderson upper and lowers, and a WMD trigger set.

Any suggestions?

June 18, 2017, 18:07
When ya going to do an.308 ?? I would like to compare a piston AR to the Impingement .308 in terms of accuracy, wonder what we would see? :)

Like the FAL I think the piston AR would flex and lose accuracy??

June 18, 2017, 18:34
a similar build to the PWS version that is quite popular

you seem to have made a good choice

7.62x39 in a piston driven AR,

nearly all 7.62x39 ammo is filthy dirty

a piston system that dumps away from the bolt/action is good

have not heard anything about the bolts from PWS but others often crack due to the decreased material thickness in the rotating bolt, keep several on hand just in case


June 18, 2017, 20:27
Might do an AR in 308, tho' not for a month or 3, plus I need to think out the carrier tilt issue with the 308 round, if it's a real issue.

The next project on the cards, is a Brit L1A1 Frankentrooper - I have a CAI neutered barrel which I need to get cut to 18"(17.3/4) and a PNG FH slot cut, the lower parts I am currently acquiring, yet to order the Coonan Brit cut, as of yet.

As to the 7.62x39 bolt failure - I did read about that, and researched it quite a bit. To be honest I forget where I got the bolts from, they were highly recommended as not fracturing - my notes back home will have the make, they aren't carpenter steel, one above(!) and they aren't modified AR15 jobbies either - we shall see how they do. I hear the LMT ones are most favoured, but are rare. Adams Arms suggested I get their light weight carrier - which I didn't yet, and probably won't.:)

The whole point of the project was to build as inexpensively as I could a rifle that used the Russian round - and because of the dirt factor, to use a piston system which is easier to clean, and it really is. The first one, I built with magpul furniture, the HG's are a pig to get off, the 2nd I used a two piece HG., easier for cleaning of the barrel, which gets blow off residue - the bcg stays very clean.

$130 for the upper and lower, including ffl fee,
the barrel 90,
10 for the delta ring,
the Mission first was 40,
the WMD Lpk 70,
FH was 35,
HG's was 60,
the AA piston was 200,
the recoil buffer assembly was 35,
bolt was 99,
25 for the CH,
hammer spring 10,
firing pin 20 - so really quite reasonable - mags 16 for the 30, 14 for the 20
- so minus mags around $850-ish. plus shipping!!!

I plan to go Hoggin' with them, a buddy wants the first one I assembled(he has the Farm), this one I will keep for a while.

The grist in the scowl, is that parts seem to be less expensive since Trump but at least the ammo cost for Russian is dipping - all is good. :beer:

June 18, 2017, 20:31
Enjoy. Let us know about the piston. I shoot mine suppressed and dirty as a pig. Get the firing pin into the primer a little deeper.

June 18, 2017, 20:49
The 7.62x39 extended firing pin is meant to be a little further into the primer - as to why it isn't always, is the issue! An even stronger hammer spring than the stronger one already fitted, perhaps - me thinks something else is at play, as to what, not sure yet - yet the problem is entertaining.

June 18, 2017, 20:52
At least we know it's alive as its puking oil like an AMF built Harley Davidson from the 1970's. I like to see oil and grease leaking out of every orifice and seam. Thank the Good Lord we have plenty of combloc rifles to launch all the combloc ammo have been (and still am) hoarding for what seems like three lifetimes. Won't ever have to contemplate forcing an AR to digest the stuff except for the rifles that get drug into LGS on occasion and if factory guns have the perfect method, place in box, attach shipping label and return to maker... Kudos on the attempt and bet you will get all your issues worked out. Would suggest as you test mark the magazines that function best and dedicate them to that build. I have gone so far as to put specific finishes on magazines that instantly identify which particular load is used in them and what rifle.


Bought multiple Reaper Buck kits and have 15 magazines with this finish and always has 110 grain tipped 6.8's.


Also did 15 magazines in Tiger Stripe and all have 6.8 spc II 90 grain Gold Dots.


Any magazine with the flat rubber Magpul floor plate has 5.56 Tubbs DTAC 69 grain SMK's.


Any magazine with Magpul Ranger Plates has M855 green tip.


Have 15 magazines wrapped in Chickenflauge which are all 77 grain SMK's and and just plain black AR magazine with standard floor plate has 55 grain 5.56 milspec. For my FAL that sits in bedside rack all 20 round magazines are now M80A1 and all 30 round magazines are M80. Same for my inch rifle that lives at work, 20 rounders are AP and 30 rounders are NATO equivalent ball. For my 1911's all 8 round magazines in pistols are Hornady Critical Duty and 10 round McCormick's are PMC Starfire. If in a crowd and have time would swap to Starfire as it expands so rapidly and dumps energy chance of a shoot through is almost zero and the Critical Duty will defeat a barrier with plenty of energy to do the job or if zombies are wearing heavy clothing they don't plug as the rubber/plastic insert prevents plugging and initiates expansion. All 40 Smith magazines are Hornady Critical Duty and a primary reason for moving to SIG 40's for daily work carry is fact they will shred a Level II or Level IIIa soft armor vest. All SIG 9mm magazines have Federal 147 grain subsonic hollow points and all High Power mags now have the pink box reduced recoil Hornady Critical Defense so wife can handle reasonably well just like all of her Colt Diamondbacks have the pink box reduced recoil 90 grain Hornady Critical Defense. M1a's and all their magazines have 168 grain SMK's, CETME's all have ZQI 147 grain FMJ and so on. Can fumble for any magazine/speed loader and gun combo that's part of our defensive weapons and am 100% sure of pulling rifle off rack or picking up handgun from drawer or end table that best suits anticipated threat.

We drill, drill, drill. Wife knows where every ammo can is in every room that has 1,000 rounds of M855 on stripper clips and magazine adapters. Once my/our rifles/mag pouches/MTM magazine storage box runs dry if we're still in the fight she crawls as deep behind cover as possible and starts restuffing magazines and pitching to me. As they go dry I throw over my shoulder toward her. We run our emergency firefight drill once a quarter when she does her quarterly firearms qualification where she has to pass the Georgia State LEO qualification course with her Walther PK380's and the old course from wheelgun days with her Diamondbacks. If change any part then there is weekly then monthly training till she is 100%. When swapped her to 5.728's took a while before mag changes became intuitive and she still has to train with standard AR's. Don't have to make her train/qualify with her SKS as she loves her "commiegun" and will ask me to sweep up all the brass on deck fairly regularly. Says it and the Diamondbacks are her favorite shooters. Am trying to figure out how to get the snake guns away from her. When discovered they are $2,000 dollar guns now would lake to get them out of duty rotation and swap for Smith 19's loaded with the Hornady reduced recoil rounds.

Yes this is a bit of a Segway but try to teach all my clients even if husband and wife choose different primaries and backups to cross train with each others weapons and develop a household defense plan and practice the mechanics of it as well. Rained most of day and I blew off work. After church put on my IDPA rig to do dry fire drills. About five minutes in wife came tapping into garage with her duty belt on and live mags swapped for magazines loaded with Snap-Caps. She wanted to run against the clock on my dry fire timer. Once a quarter we practice our fire drill. Each have Nomex firefighters turn out gear upstairs and down. If in bed and alarms go off we automatically step in boots, pull up pants, suspenders over shouders, put on coats, Nomex hoods and every other cycle practice fighting a fire or escapimg a fire gome out of control. Everything has its place, everything is standardized and it all gets regular training cycles. If I tell wife to throw me a 6.8 mag odds are 90% if have Tiger Stripe rifle will get a Tiger Stripe magazine. Why excited about my DSA custom Tiger Stripe heavy barrel build as will do a couple dozen metric FAL mags in Tiger Stripe and integrate it into one of the "hide locations" stationed around the house for engaging exterior threats. Even when wife is weak and using wheelchair it's a rolling gunship and the back and bottom are NIJ Level 3a. If we are out in public and world turns to crap can put her on ground and turn chair on top or her or lay sideways and she use for cover while providing covering fire for me.

Once a quarter I done one of my rifle rated kits, turn on radios and walk out door into the darkness. Wife has to fire at least one transceiver up on active frequency in my ear along with digital trunking scanner. She also either goes to radio room and fires equipment to give live sit-reps (a big challenge if not already running) so normally grabs a thermal and peeks out front and back looking for targets to put me on. If I were to get engaged she is trained to put accurate fire on threat if possible, if not at least provide covering fire when I move. We do the same with emergency medicine, I always know where multiple Epi Pens are for her and she knows where my stress dose steroids stashes are upstairs and down. Would not trade her for all the tea in China. Even though getting more physically challenged every year she is better prepared to carry her own weight amd support whatever task than 99.999% of healthy young women in this country unless it's shopping at the mall.

So sort and mark your magazines, prep your homes, train your wives/husbands. She knows Halon from ABC dry chemical extinguishers. Knows how to turn radio on and use headset. Can reload magazines even if get down to the big box of 45 acp cast by sofa that we are perpetually wiping down, dropping in chamber checker and boxing for range at work. Of all people my mom mentioned worry about greasy fingerprints causing cases to corrode if stored long term or just one more easy peasy piece of evidence for the Revenuers if unable to police up brass before un@$$ing the A.O. ever since wear a thin white cotton glove on hand feed brass into Dillons, then when each box comes upstairs wife and I put on cotton gloves and wipe down each round with clean cotton cloth looking for high primes, shaved lead, split case didn't see before loaded then wiping well, dropping in chamber block then boxing up. She loves this stuff as realizes irpts a mean cruel world. Between a Parliament Funkadelic concert turning into a riot involving gunfire twice on the Chocolate City Tour, getting lost in Sharia Law neighborhood in Paris, bad scene on Sunset Blvd in Hollyweird, and cop following her home from work and when would not open door he tried to kick it in. She was astute enough to have 911 on the phone and put a round of 38 through door of her house (before we married) and cop was caught leaving her driveway and eventually tied to multiple rape, assault and kidnapping charges. Watched her break a pick-pockets arm on a Paris subway and until bone disease started eating her inside out was toughest chick I ever knew.

So as I was advised in Gunsite thread that more gins is not necessarily better, training is, we do it. Being able to keep track of ammo, magazines, accessories and which gun they mate with have it covered. For that matter if we run wife's two AR's dry with 50 rounds each, both SKS's with 20 each, both my 6.8 AR's, both 5.56 AR's, FAL, CETME, M1a, scatter guns all dry and have to do a single reload the world has turned to crap and we might be in over our heads. If fire alarms, automatic fire suppression and handheld firefighting equipment doesn't knock a fire down or at least get us out the door know we died fighting. Wonder what percentage of households have at least five or six "most likely" scenarios prepped for and do regular training to mitigate? I know lots of guys whose wives think such is lunacy and won't participate in even basic training. My biggest growing client base for tactics are doctors with their wives and people that live in high end communities with high level corporate jobs. Currently church security teams is eclipsing all,but that bubble will burst soon. Sort your magazines, test your ammo and guns, train all household members and harden structures. Worst case is you never need it but everyone learns family teamwork.

June 18, 2017, 20:57
The 7.62x39 extended firing pin is meant to be a little further into the primer - as to why it isn't always, is the issue! An even stronger hammer spring than the stronger one already fitted, perhaps - me thinks something else is at play, as to what, not sure yet - yet the problem is entertaining.

Take measurements. You already said it was dimpling. I had to extend the pin .about .010 to get it to hit 100%. No heavy hammer either,

June 18, 2017, 21:08
Sounds like your household is well sorted - good for you and yours Hueyville - my Ex couldn't boil an egg, let alone change a light bulb.
Reading the inter webs, it does seem that AR 7,62 x39 mags are an issue - I may very well rid myself of the ASC 20 round mags, the C prod mags are way better, just have to get them to function with the heavier soft point round reliably before I go Hoggin'. The AR's I built in 5.56 function flawlessly, FN barrels and their accompanying bcg's swallow anything I feed them - no steel case in those!

June 18, 2017, 23:51
i noticed that mine with 154 strings vert to.

June 19, 2017, 08:18
I did an x39 AR. It was midlength with an AA piston. Short stroking was the culprit. Drilled the gasport to .125, worked the 6 oclosk of the barrel extention, lightened recoil spring and piston, used AA light bc, worked all mags for smooth feeding, wolf spring, long firing pin, MGI Hydra super bolt. Runs great!!
Rings 500 yard steel mag after mag!
Experts all said not to waste money on this, they NEVER work. I enjoy mine. Works well.

June 19, 2017, 17:40
have 3 and all run, i'm getting out of 223

June 19, 2017, 19:23
Well I won't be able to measure the Fp protrusion until I get back to Atl.- the one I have is meant to be the extended type for 7.62x39 use, so slight dimpling does seem strange - the weaker buffer spring notion in a 7.62x39 AR., does seem counter intuitive, can someone explain that to me please.
Then feed issues are likely a combination of magazine and feed ramps. I will see what is left to remove, and a careful comparison of the ASC, and the better C prod mags will be in order - anyway thanks for the input, I will keep up, as time allows, with updates.:)

July 21, 2017, 15:37
Out at the range today - took the AR7.62x39, and an Imbel on Imbel. The Fal is just great - Port and Stg ammo, she loves the STG, the Port not so much! Different POI - up and to the right by 2". Left it zero'd for the Austrian Stg.
Anyway after much mulling and musing I decided the last week to get the Dremel out and work the AR Mags.
The 20 round ASC mags were the real issue on reflection, and dug out some metal on the mags. Two areas, the front where the round launches up into the chamber I ground a deeper section, and on the sides between the two lips, to conform to just the vertical walls of the mag body, so the round was freer to move up and forwards without catching.
<iframe width="560" height="315" src="https://www.youtube.com/embed/ZIxAEbSuMhc" frameborder="0" allowfullscreen></iframe>

And then this below for the 30 round C-Prod mags! Hammer time!

<iframe width="560" height="315" src="https://www.youtube.com/embed/2FntJSnPo_c" frameborder="0" allowfullscreen></iframe>

300 rounds later, no fail to feeds, no dimpling!

So now, happy happy joy joy - the AR in 7.62x39 runs flawlessly! Problems solved! :D

July 21, 2017, 17:20
So if I'm building a 7.62x 39 ar pistol and would like a piston is that possible? I got a 10.5" barrel with a carbine gas system. Would I just use a normal aa carbine length piston kit?

July 21, 2017, 19:14
I used an Adamsarms carbine kit, drilled the Gashole to 1/8" - my barrel is a 16" Carbine from Delta team tactical - the melonited one! No experience with a shorter barrel to be honest, though I do seem to remember coming across a few in my research phase, that of people having had success in building them, with a Carbine barrel cut down - spent gases and gashole diameter, and all those good things come to mind. Give Adams arms themselves an email, ask them directly as to what they suggest or have experience of. Joe Bob's recently had the Carbine AA kit for $199, if they have them still, others on the 'Net will - especially in this market, unless you have one already. Let me know what you find out - always tinkering and the Russian round is fun to shoot - at 20 cents a pop!:biggrin:


They don't do a 7.62x39 pistol kit but they do a AR15 in pistol - gashole diameter I bet is it, that and the 6 o'clock finger removal between the feed ramps might be all - that and the mag issue! They will want to sell you their lightweight carrier !

August 07, 2017, 21:38
Agreed. Something to keep in mind about sampling the gas to run the gun. Mine was midlength. You say you are using carbine length? Test the system BEFORE drilling the gas hole (love saying that). Seriousely. Sampling gas pressure at carbine length will be higher than at midlength and god forbid, rifle length. Problem is disproportion between cartridge volume and bore volume. I have noticed D.I. versions run best on pistol length gas systems. So it is likely that you wont need to drill up to .125" to bring the system into balance.
And yes AA does not list this as a cartridge option with their kit as success is far from guranteed and experience and knowledge are required to make this build run. NOT DROP IN.
However Cody was very helpful whilst i was developing this rifle.
This build is VERY much worth your time. Everything you need to be aware of for success is referrenced to in this thread. Good luck!