heavy subsonic 7.62x39 load that will reliably cycle a semi auto

[Tackleberry41]

Im looking to build an upper. I know most are going into the 300AAC for a suppressed weapon. But Im not completely sold on it. Book data puts it a step behind the x39 supersonic. Latest hornady book shows you need to go to 110gr in the 300 to equal velocity of a 123gr x39. 300 is not exactly cheap compared to a 5.56 or x39. Any gun shop will have a pile of 5.56 or x39, not so much 300. It would be another set of dies to go out and buy, and powder to buy I do not have on my shelf.

I already load for x39, and have a pile of it ready to use, vs going out and stocking up 300. I know the x39 is not the most reliable in an Ar15, need the right mags, maybe some gas port work. And are known to mess up bolts.

Question is, is there a heavy cast x39 load that will cycle an AR reliably? I load plenty for subsonic use, but in single shots or bolt actions, so cycling has never been an issue. I can get the NOE 230gr 311 to stabilize in a mosin subsonic, but may be pushing it for length in an AK, I have 2 200gr molds.

Or just bite the bullet and go with 300AAC?

[Electric88]

I can't offer any input on the subsonic x39. But I took the plunge on the 300, and don't regret it. Reloading for it is a little more involved, but I don't mind the extra time spent doing it.

Just the call that my tax stamp is approved, so I'm off to pick up my suppressor this week :D

Whatever you find out with the x39, I wish you luck on it!

[lotech]

I don't have my notes handy, but did some cast work with a couple of SKSs years ago using much heavier than normal cast bullets and somewhat reduced loads. I don't recall now if I used the 200 grain+ loads that I also used in a couple of Ruger bolt-actions in 7.62x39. However, I had no difficulty getting my loads to reliably work the action. I would think an AR-15 would be similar in this respect, though I'm in no way comparing that design with the crude SKS.

I'll attempt to find my notes as I'm curious now. Perhaps others on this forum have experience in this area.

[runfiverun]

what's your twist rate?
in my AAC's it's 1-7.
this allows me to fling the 200 whatever Lees boolit is [30-40?] at pop noises velocity with 3.5-4.0grs of powder.
I don't gotta worry about a bolt clanging back and forth.

I have worked some jacketed sub loads for an AR upper and they worked flawlessly I could have actually went lower with them but I wanted to err on the working for sure side to get started.
anyway for the AR's I'd go with the shorter gas tubes [pistol or carbine length] for sure and maybe a lower weight bolt group if you really wanted to go slow.

I mostly poke my 300's out with a couple of different loads.
a 100-110gr varmint load for stuff in the spring.
a 150-165gr cast load at 1500 ish for most target and fun shooting work.
and the heavy boolits for poking holes in paper at 50 yds.
the barrel never gets hot and I just tumble lube them and they don't use enough powder to ever see the cup I scoop from go down.

the wife really likes the 311359 in hers for everything.
she shoots paper, rocks, and varmints all with the same load.
it's in the 1650 fps range and is accurate out to over 100yds so perfect for her skill level.

[Tackleberry41]

Barrel listed on Midway for example is 1-10 twist. Would expect it to work w 200gr easily. Not like I plan to burn thru alot of subsonic. Just be nice to be able to use it, and rifle work.

I went by my local shop to get an idea of what they stock. Thats a big thing is getting ammo. Yea it can be ordered or loaded, but whats easy to buy? They only had 2 flavors of 300AAC, a remington subsonic, at $34/20. A bit steep, and not impressed with it, somebody I know was shooting some one day and it was blowing primers. The other was a 125gr, a little more reasonable at a little over $20/20. I have enough reloading projects to be spending the time converting a bunch of brass. 7.62x39, I can just crack open an ammo can, 300 I would have to go buy ammo just to shoot the rifle.

[rda72927]

I have enough reloading projects to be spending the time converting a bunch of brass..

It's a waste of time to convert 223 to 300 BKO, just order it. There are several folks doing to conversion. Last batch I purchased, 3000 pc for 300.00. I can't make it for 10 cents each. I think his price was 110.00 for 1000.

I have always had a harder time finding 7.62x39 brass that was boxer primed.

[runfiverun]

you can get it right here from Grumpa, Matt knows the stuff inside and out.
or just buy already converted 223 brass for like 170 @ K from brass guy's.
Federal makes it, Hornady makes it, SSA has it, and so does a bunch of others.

I load mine on a Dillon 550 using the 223 plate and the 30 carbine powder funnel.
it reminds me of loading a 357 case necked down to 30 caliber.

if I were ordering an upper for the 300 I'd look for a 7 twist, but if all I could find was the 8 then I'd limit myself to 200gr boolits.
or just buy the Ruger American like I bought the wife. [about 300.00 plus scope]
it accepts every 30 caliber mold I have tried in it so far and it doesn't quibble about brass or load details.

my AAC made one has a lot tighter tolerances and it shows on paper but it is a lot more finicky about molds and cases.

[Tackleberry41]

As usual a thread goes off track, ask about 7.62x39 and its all about the 300AAC.

[runfiverun]

sorry man I thought you were comparing the two.

your AK is gonna need gas volume to cycle the action.
about all I got is try something like 10grs of 4227 with your 200gr boolit and see what happens.
I know that combination will cycle an AR 100% and keep everything on the down low speed wise.

[Bloodman14]

Not a fan of the AR-15/M-16 platform (carried one in the Army), but in my Yugo SKS, 1.4cc's of LeveRevolution behind an NOE 316299 Mod GB cycles just fine, and doesn't throw brass into the next county. Maybe a starting point for load data for a x39 upper for your AR?

[Tackleberry41]

I simply have an extra lower, bought 2 of the 80% ones. One was a blemished billet unit for $30, other unfinished forged. The billet one has a basic 16in carbine set up, no need for a second one. Got one of the AR stoner kits from Midway. Had a guy who was going to put together a really nice upper thru his shop, but didnt come thru. It goes bang, bullets go where I point them. Considered a 9mm, but they are extra pricey for whatever reason, and bit big for a 9mm carbine. So looking at other options. I am not messing with 300AAC due to the expense of buying ammo, brass, dies, etc. I have a huge pile of stuff that needs loading as it is. Havent ruled out 7.62x39 yet. But might just build a 5.56 rifle upper, get a nice trigger for it.

[runfiverun]

the x39 in the AR usually tends to be a pain.
I looked into it and it all seems to boil down to the magazines.
some work some don't and they can be glitchy from the same batch.
I never got around to the 300 upper I kept buying ar's for and finally went bolt rifles.
I don't regret the decision.
I'm okay using my heavy barreled AR for varmint shooting, the 300's as 300's and using my sks's for the cheap steel cased ammo blasters they are.
I still want a good x39 bolt gun since I have all the stuff just sitting there to load for the round.
anyway that's the direction I finally went.

[Boolit_Head]

Not so much the magazines as the taper in the case requires the distinctive banana curve of the AK mags. That is what makes it a no go in normal AR mags or the design. Some have dedicated lowers with drastically different mag wells and mags just for the 7.62x39 round. That's what makes the 300 shine in the AR platform as it only requires a barrel change.

[2wheelDuke]

I'm guessing it's possible, but there's a whole lot more data out there for the 300 blackout. You may want to look into an adjustable gas port to give you a little more versatility. Getting the x39 to run both subs and supers reliably will take a fair bit of tinkering if I had to just guess at it. And adjustable block will allow you to un-do it if you open your gas port too far.

[35remington]

If you don't care about feed reliability it's doable in a conventional lower. The round really needs a more curved magazine.

[Digital Dan]

As usual a thread goes off track, ask about 7.62x39 and its all about the 300AAC.

Well, you raised the issue here:
Or just bite the bullet and go with 300AAC?

Dunno what your fascination is with ss velocity differences, they are both mediocre at best and neither present as Thor's Hammer. Few extra fps for light .30 cal bullets is meaningless. If you want to find success at subsonic velocity, precision is your friend. OTOH, if you just want to rationalize doing this with a 7.62x39 you don't need anyone's help to do so.

[Mica_Hiebert]

DO NOT LOAD THIS WITHOUT FURTHER RESEARCH!!!!!
I have read that a load of H110 around 10-10.5 grains under a 200-220 grain bullet will get subsonic velocity with enough pressure/gas volume to cycle a semi auto in the x39 but h110 is dangerous to experiment with so I would research a little more before trying it.