16” 7.62x39 Short Stroke Piston System
A few months back, in the beginning of 2018, I traded an Optic I had for an Adams Arms Low Mass Bolt Carrier – Carbine Length Piston kit. I already owned an Adams Arms AA-15, I wasn't using the entry level optic (about 140 dollars) and decided that the swap would be a good one to, at the very least, have piston rod/block/spring replacements.
While sitting and mulling over what I should do with the expensive part of the kit: The Low Mass Carrier, I wasn't sure if I should run it in my AA-15, create a whole new build, or what. For a very long time, I had had interest in building out an Upper in 7.62x39. I know I didn't want to spend more than an Entry level AK, as, that would just be foolish in the long run economically.
For this rifle, I really just wanted an easy going plinker. I wasn't looking to build a fighting rifle, or competition gun. I really just wanted to finalize a full build of a stripped lower and upper. For the pride, joy, and success of putting in the efforts.
So, keeping in mind this is a budget rifle, I have the following companies Frankenstein'd into this rifle:
Upper:
Stripped BCM Upper w/ Dust Cover and Forward Assist - $65.00
Bear Creek Arsenal 16” 7.62x39 Barrel .093 Gasport - $75.00
Bear Creek Arsenal MPI/Headspaced Assembled Bolt - $45.00
Adams Arms Low Mass BCG and Adjustable Gas Block - $140.00
Adams Arms Handguard - $0.00 (Takeoff from another rifle when I swapped my 5.56 to a MOE SL)
Cost of Upper: $325.00
Lower:
Anderson Lower - $40.00
Stag Arms Parts Kit w/ FCG - $32.00
K-Grip - $14.00
VLTOR A5 Tube / A5-H3 Buffer - $40.00 (Thanks to a great member here in the Equipment Exchange)
Cost of Lower: $126.00
Total Cost: $451.00
Overall, I stayed under the 5-6 hundred dollar budget that I know an AK would be at; I also had a lot of these items for months and months.
I had the sight I traded back in January since 2015. I have had 4 Anderson Lowers bought back in 2016, from a member here on the Exchange, again a very good deal. I still have 2 fully built lowers without uppers. The Stag Arms Parts I picked up during Black Friday as they had an amazing deal.
The rail is the hard part. I had hoped one I had would work, but not currently. I have a round handguard cap that I had to modify to accept the piston. Than I can add my own standard carbine guards or try the BCM PKMRs (I tried it, they don't work. Good news is, my pistol just got a new set of PKMRs on it). One of the biggest detriments to the Adams Arms Kit is the handguard compatibility. It only can utilize Samson free float guards or only about 50% of handguards that are “drop-in” and still use a standard barrel nut.
The BCM upper should speak for itself, but I must say, the Bear Creek Arsenal extension was sized as if it was built for the BCM upper. It was a super snug fit, but not one I needed a mallet or heat gun for. A light pressure and some wiggling and it pressure fit in very nicely. I have a relative with a truing stone for the upper and after running the truing through, it was an immaculate fit.
I picked up two different magazines for the rifle:
1x ASC 20 Round Magazine
4x C-Products 30 Round Magazine
I tested both magazines with single rounds, multiple rounds, and full.
We had Bolt Hold Open success with all of them.
The mags drop free very well, except the ASC. Overall, I am not too worried about it.
When we talk about the gas system / BCG, this is what really sold me on the 7.62x39 build. The research I read, across multiple sources, insisted the 7.62x39 round is “low pressure” in comparison to the .223/5.56. When I heard about this, and the problems it comes with, I did some digging. I noticed that many were having difficulties with springs being too powerful, or the mass being too high for reliable extraction and stroking. When I saw that low mass carriers were a big help in tuning these rifles, I knew I was interested and in the right direction.
I am, supposedly, supposed to be receiving an adjustable gas block from Adam Arms any day now. They reported issues with the XLP gas blocks seizing up. They advised me they would send out a replacement block in honor of warranty. I threw this one on to test operation, to see if the gas was ported well enough for the standard piston gas block. It sure is.
It runs very well so far. I have put a couple hundred through it, and the most notable piece is the impulse being extremely different. I have not had any hiccups due to weak springs / hard primers. Keeping my fingers crossed.
Nonetheless, this build has been a crazy adventure. I will post my build photos below and will post up a video of operation soon. Thanks for all your time and energies reading this build.
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Originally Posted by sasquatchoslav
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