7.62x39 subsonic questions

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Precision
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7.62x39 subsonic questions

Post by Precision » Fri Jul 12, 2019 8:09 pm

I am looking to load 174 to 180 gr bullets in a short barrel AK pistol as subsonic velocities, 1000-1050 fps. The pistol will have the option of being silenced.

I am looking for experience / load data / what not to do.

The goal is for reliable cycling with or without the can. The purpose is for an article about making such guns effective home defense guns and how to load for that concept. I am having difficulty finding subsonic load data.

I have all kinds of load data for 150gr supersonic, which is another option, unsuppressed.
Thanks guys
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Cobar
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Re: 7.62x39 subsonic questions

Post by Cobar » Sat Jul 13, 2019 12:24 am

Way outside my knowledge base, but I look forward to what info you get.

Let us know when the article goes up.

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Netpackrat
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Re: 7.62x39 subsonic questions

Post by Netpackrat » Sat Jul 13, 2019 6:07 am

Reliable cycling should be the least of your concerns. The AK rifling twist rate may not adequately stabilize heavy bullets at subsonic speeds. There is a reason that .300 Blackout is rifled at 1 in 8" or faster. AKs are closer to 1 in 10". That may be enough for a 180 grain bullet at .308 speeds, but subsonic is a whole different ball of wax. For sure test any subsonic loads on paper at 25 yards and reject if there are ANY signs of keyholing.

And you probably already know this, but unless you are running a can specifically designed for the AK (which will generally have a larger bore for more clearance through the baffles), The odds of getting a satisfactory alignment on an AK are not good. There's a good reason why many reputable can manufacturers will not even offer their products in the thread sizes commonly used on AKs. Not only are the threads frequently not concentric to bore, the design doesn't provide for a good shoulder for the can or a QD mount to bottom against.

There are a couple of approaches to dealing with the alignment issue, the first is that you can buy a can like Dead Air's Wolverine, which is specifically designed for the AK, and has a larger bore clearance to compensate for any misalignment. The second is that you can build the AK specifically to work with a standard can. I have taken the latter approach with my SBRed AK... I built it using a new US made 16" barrel but to AMD-65 dimensions with the shorter gas system and the front sight block set way back against the gas block. Then I pulled the barrel back out, and took it to a gunsmith for shortening and threading at 1/2-28. It is ever so slightly longer than an actual AMD-65 barrel would be, because it sticks out from the front sight block far enough for the barrel threads to have a real 90 degree shoulder. If you buy a new AK barrel it will most likely come with an angled shoulder, like the originals.

As far as reliable cycling goes, if I were trying to run subs in an AK, I would start by coming up with a load that did what I wanted it to do and stabilized properly, and then make the gun run it. AKs tend to be overgassed to begin with, so there are good odds it will run without having to do anything special. Especially once you have the added back pressure from a can. Probably start with A1680 powder like many of the .300blk sub loads use; it will probably generate more gas pressure at subsonic velocities than most of the other choices, and it's also one of the better powders for supersonic 7.62x39 loads so getting some is not a waste either way. And don't expect miracles... The AK is a noisy action no matter what.
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Precision
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Re: 7.62x39 subsonic questions

Post by Precision » Sun Jul 14, 2019 1:30 pm

Thanks NPR.

I think for our test purposes we will be using a can that is significantly larger (internal channel) than .320.
I was unaware of the shoulder angle thing. Good to know. I have not run stability calculations for subs, but my research seems to indicate people like runnning 210gr or heavier which seems odd to me from the stability angle.

The powders I have seen info on are A 1680, A 5744 and Trailboss. Trail boss seems to need compressed loads and it is specifically stated to NOT be used compressed, so that is likely out. I have seen mention of Clays, Red dot, universal and a few others; but with scant info and I am not looking for low powder volume induced Secondary Explosion Effect.

I ran some rough stability calculations and it looks like with one of the guns (1:9.5 twist) 180ish grain bullets are quite stable. Pushing into the 200 gr range is mostly stable and getting into the 230 gr range is getting dicey.

I am looking to experiment with some Hornady and Speer 180 gr RN SP bullets and a 190 gr from Maker Bullets that is specifically designed for suppressed use in 7.62x39 and will expand down to 850 fps IIRC. My velocity goal is 1050 fps at the muzzle with the subs. Roughly 2000 fps with the supers.
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Netpackrat
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Re: 7.62x39 subsonic questions

Post by Netpackrat » Mon Jul 15, 2019 1:31 am

As a point of reference, 300 Blackout will not reliably stabilize subs heavier than 220 grains with the standard 1 in 8" twist that SAAMI calls for. The guy who wrote the spec, later said if he had it to do again, he would have specified 1 in 7" instead (which is what my guns are).
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Precision
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Re: 7.62x39 subsonic questions

Post by Precision » Mon Jul 15, 2019 6:35 pm

Thanks.
I have been looking at 300 BLO for baseline numbers and concepts. It really looks like anything over 180 gr is not likely to be suppressor safe as far as stability goes.
Neither the pistols nor the suppressors are mine, but we will make sure to do all tests at 10 and 25 yards before we run them through a can.
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Netpackrat
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Re: 7.62x39 subsonic questions

Post by Netpackrat » Thu Jul 18, 2019 11:15 pm

Ran across this just now:

https://www.sgammo.com/product/prvi-par ... -line-ammo

Description says it does not cycle semis.
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Captain Wheelgun
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Re: 7.62x39 subsonic questions

Post by Captain Wheelgun » Fri Jul 19, 2019 10:47 pm

Netpackrat wrote:
Thu Jul 18, 2019 11:15 pm
Ran across this just now:

https://www.sgammo.com/product/prvi-par ... -line-ammo

Description says it does not cycle semis.
I saw that on TFB, thought that it might make a nice baseline to work from. I've been thinking about getting a Ruger American in 7.62x39 to go with my Mutant so I can play with subs and other odd loads.
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Netpackrat
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Re: 7.62x39 subsonic questions

Post by Netpackrat » Fri Jul 19, 2019 11:04 pm

Wanting to run subs is pretty much the whole reason I ended up with ARs in 300blk; it is the easy button. Should still be do-able in x39 but getting it right can't be done cookbook fashion like 300blk. One thing that is good is I discovered that my ancient RCBS powder measure that I have fought with for years, happens to meter A1680 with Total Accuracy. So I was able to load up a shit ton of subs for my 300 bolt action last night. All of the factory subs that I have been able to try go supersonic in the 16" non gas operated gun, so handloading was really the only viable solution for it.

with x39 the twist limits you to the lighter bullets, which makes it harder to generate enough gas pressure to still cycle the action. I still think it is do-able given that 300blk subs can still be made to function in the 180-190 grain range, and most/all AKs are overgassed, but it will take some work and powder selection is going to matter a lot.
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Precision
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Re: 7.62x39 subsonic questions

Post by Precision » Sat Jul 20, 2019 7:10 pm

The easy button is easy. That is why I get paid to write articles about the not easy button. It is also more fun. Oh yeah and I already have the easy button covered.

Thanks for the help so far. I will see where this leads. Perhaps it will help you a bit.
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