Reliable AR15 Subsonic Loads? (7.62x39, .308, 1:10 bore)

[gojckent4]

Okay, so I know some of you have been beating this old horse since before 2003. The most recent post I can find [here] was in 2013, which was on a dead 2003 thread last active in 2006... BUT, I actively reload for all my weapons so I'm comfy testing. My first AR was a 10.5" 300BlackOut, and I get it, 300Blk is cooler, but it's time-intensive to replace and expensive to buy. I'm willing to invest the time to finding at least one subsonic load that's powerful enough to cycle/lock-back the bolt.

After my research, I realize this is an emotional topic for some. I can learn from those of you who have experience with making up your subsonics for SKS, AK and bolt guns, but please don't take this thread off topic. I'm after as many SAFE and effective subsonic loads as I can find for the AR in 7.63x39. I found http://www.EBRammo.com, where they sell the 220 grain "Ghost" ($41/20) and "Jackhammer" ($32/20) rounds. I'm a 27 year Army vet, and there's ZERO fun in buying anything pre-mixed expensive ammo. Unless, maybe, it's also a tracer...

Peter Cronhelm's research at http://members.shaw.ca/cronhelm/DevelopSubsonic.html no longer exists. If you have a copy, please PM me - I want to build on other's work. I found references to widening primer holes to 9/64 so powder burns more evenly. Also, to using "fast" pistol powder vs "slow" rifle powder, and adding tissue between the powder and the ball. Most everything I've found is old and relates to AKs, SKSs, or bolt guns - all of which are relevant for study, but different, and maybe even dangerous in an AR.

The test weapon will go into my SHTF footlocker with repair parts, these sub reloads, and cml ammo. Components are:

~BAFE upper receiver with PSA 7.62x39 BCG, enhanced pin, and generic upper parts
~Cerro 80% lower with PSA polished-FCG and a Thordsen/MFT cheekrest
~ARD 7.5" 7.62x39 melonited barrel
~Bore: .308" with 1:10" twist (yes, I know - but testing for yaw up to 200grains @ 100yards)
~C-Products Mags
~7" quadrail with flip-up diamond sights - maybe a scope if tight groups
~My can, when approved and built, will be 7"x1.5" Titanium and SS (I don't do mag dumps)

*Modifications (done): Blended M4 ramps into one [ugly] ramp, enlarged gas hole to .125", dimpled to secure gas block, slugged to confirm .308 (gtg). According to NFATracker.com says my 30Jun16 trust-eForm1 should be here any day...

Wolf steel case ammo cycled/fed fine and was accurate @ 25y - ejects hard at 3 o'clock. Will test at longer ranges later (backyard is a 7-200y wooded gong-range). Pulled two types of Wolf lead and measured 123gn and 124gn, both with .309” diameters (expected .311). Didn’t recognize the powder, but it’s 7mm-ish and tubular like pencil lead.

Found lots of posts on several boards for subsonic in x39, but few addressed ARs. Most said "x39s as subsonic is a lost cause" (with AK gas most likely). Some had success loading 200gn SP backwards (bolt gun most likely). No posts showed repeatable testing process or good documentation, most comments were all mixed together and confused between platforms (AK, SKS, Bolt, AR referencing Brit .303 and/or .308 thru .311).

Any help will be appreciated, but PLEASE don't take us down a rabbit hole or quibble about this never working. I’ll report back with whatever I/we find. If I blow my head off, my wife will let you know... There MUST be other shooters out there with ARs and short x39/.308 barrels (and suppressors) who want this to work

Thanks in advance for sharing your experience!

[T-Rex]

I went down this road in oh about 2003-2007
I used a 1:10 twist, 10" barrel
I could never get a really consistent load or velocity, w/o using a filler. Not that it's a terrible thing.
The hardest part was finding heavy enough projectiles to stabilize and be worthy of subsonic flight. Not a lot of options in .311/.312
There was a stint where I was casting, but I was never happy w/ the results.
I didn't find that opening the flash hole really did much, at least not for me.

I sold the barrel and bolt, replaced the chambering w/ 300Blk and I'm building a dedicated suppressor for it, possibly this year.
I use 9.4g of H4227, behind a 240g FP Leatherhead, coated & cast bullet.

My endeavor did not end there.
I picked-up a used Savage 10 in 223. Opened the bolt face and chambered it in 7.62x39mm.
The difference was, this time I used a 1:8 twist, .308 rifled barrel. Now I can shoot heavy subs, be it jacketed or cast, and have plenty of designs to choose from.
I'm currently using 8.2g of Universal to push a 220g RN bullet. I still need to use a bit of filler, but that will be unnecessary as soon as I finish the integral suppressor for it.

[0101silent]

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