Subsonic 7.62X39

[Afalex1]

I have an AR15 in 7.62X39 with a 1:10 twist barrel. I have been kicking around the idea of playing with subsonic loads with it just for fun. I have googled it a bunch and have come up with a handful of possible loads, but I wanted to pick the brains of the members here first.

I am looking at using a 200 grain sierra SPBT loaded backwards into the case to help with stabilization (intent is to eventually start casting my own 180-220 grain soft lead alloy bullets and I understand lead bullets naturally lubricate the barrel more than jacketed and there are other benefits with lead when loading light as compared to jacketed). I have read about using Red Dot powder and drilling the primer flash holes out to 9/64" to aid in an even primer flash and reduce the chance of detonation from the primer flash going past the powder charge and igniting the powder from both ends.

I was wondering if anyone with QuickLoad or similar software could run some numbers for me. I plan to use a CCI LRP, winchester brass, sierra game king 200 grain SPBT, OAL 2.200, and 6.0 grains Red Dot.

I don't know if and don't think this will cycle the action of an AR15, but it would be neat to see. But I also don't want to blow myself up trying this. Red Dot is a high volume powder so I think even a 5.0 grain charge would still be safe, but this is where I need load software to test the percentage of load volume in this case with this bullet and powder.

Amy help of insight will be much appreciated.

Thanks,

Alex

 

[DDriller]

10- 12 grains of Rel 7 should get you around 900 - 1000 fps and may cycle. 6 grained red dot should be in the 1000fps range.

 

[Afalex1]

Driller,

Have you tested those loads before or are they from a loading program?

Thanks for the info.

 

[DDriller]

Those numbers came from QuickLoad. Very similar results to what I get from my 30HRT that I have tested. Interesting the case fill on both powders was almost the same at 54%

 

[Afalex1]

Would it safer to start a grain higher and work down. 50% density makes me a little nervous. But, I'm hesitant to go higher because of how fast of a powder red dot is. I have seen 6 grains of red dot on other sites too, but they have been with 180 grain loads.

 

[DDriller]

You will get many differing opinions on load density, a lot of pistol loads are lower than 50%. I personally try to get around 80% density for all my loads if possible as recommended from Marty Ter Weemes of Tepppo Jetsu when I got my .338 spectre from him. There have been a few cases of flash over KBs with low density loadings but they can very rarely be repeated in labs. I shoot 60% loads in my 30hrt with no problems. Trade of you deal with using higher load density is typically more un-burnt powder which I don't like running through my cans.

 

[Afalex1]

Good info and thank you for the help.

I loaded a dumby round with the 200 grain sierra game king seated backwards at 2.2 OAL. It wouldn't chamber in my AR15 because of the extremely blunt tip. I loaded up six with the 200 gn loaded forwards at 2.2 OAL, 6 grains red dot, CCI #200, and once fired Winchester brass.

I loaded one with powder and the bullet loaded backwards to give it the old redneck shake check to compare load density. The bullet with the bullet loaded backwards had a lot more powder shaking around then the one loaded forward. (I understand this is not scientific in anyway and is just a mere musing). The 200 gn Sierra game king barely loaded to 2.2 OAL with the case neck and crimp landing right at the edge of the ogive.

The rounds feed in the action, but I don't have any clue how they shoot, group, stabilize, or if they will cycle the action yet. I will wait until I have a little down time to test these loads at 25 yards. Gotta make sure I write down good data and pay close attention to pressure signs and keyholing.

 

[Afalex1]

I went and shot these today. I was at 25 yards and they impacted about 6 inches low and 2 inches right compared to my normal rounds of Tulammo 122 grain HP. Zero pressure signs at all, no sonic crack or bullet noise at all, and does not hurt the ears to shoot without hearing protection. However, it did not cycle the action. I did not really shoot for a group. I loaded 7 rounds. 1 was shot holding the gun as far away from me as possible with a table and other things between me and the gun. Just a little insurance if it went south. 3 were fired at a target off hand and 3 fired at a railroad timber to see if the bullet would pass through the corner of it and expand at all. The bullet went into the railroad timber, but did not exit. Its path should have made it pass through about 6" of it. It is a pretty dense material so I would have been surprised if it made it through. I doubt the 200 grain sierra game king would expand at sub sonic velocities anyway.

Now to keep trying to find a powder that will cycle the action at least a little. I doubt it is possible with a 7.62x39. Part of me wants to up the charge of red dot .1 grain at a time until I see pressure signs and I hope they don't spike so quickly that it hurts something. I need more bullets first. These were just old randoms I had laying around.

 

[DDriller]

. 1 was shot holding the gun as far away from me as possible with a table and other things between me and the gun. Just a little insurance if it went south.

LMAO I have a cement wall I stand behind and just stick my arm the weapon around. No kabooms but I have ruptured a case or two. Damn wilcats!

 

[Afalex1]

yeah, I know a table wouldn't do much, but it made me feel better. I was testing these loads in the back 40 of a pecan orchard.

 

[rob072770]

Alex let me know what you work up as I am suppressing my 7.62x39 upper. Do you plan to hunt with them?

 

[Afalex1]

No plans to hunt with them. Just playing with different reloads. I don't think a sierra game king will properly expand at sub speeds and will not easily take down game. I might use it for skunks and coons just to see what it does.

 

[Hard_ware]

AA1680 is what I had to use to get the 300blk to cycle. I used 11 gr with a 220gr sierria pill

 

[Afalex1]

Thanks hardware. I know 1680 is used in the x39 for supersonic loads and is one of the best for it. Anyone care to check load density in quickload for me? Wanting to stay above 50%.

 

[DDriller]

10.8 gr powder 53% with 220 gr SMK. 1080fps
10.9 gr powder 49.4% with 200 gr bullet 1083 fps

 

[Afalex1]

pretty close to the edge for me. 54% with the red dot was a little scary to think about. I guess I need one of those concrete walls and a gun I don't care about to proceed any further.

 

[DDriller]

14.6 gr Rel 15 will give you 69% fill
16.6 gr Rel 17 will give you 75% fill
15.5 gr Vihtavuori N150 will give you 77% fill
All based on 16" barrel and 1050 fps 200 gr bullet

 

[Afalex1]

Those all look promising. Thank you.

 

[rob072770]

pretty close to the edge for me. 54% with the red dot was a little scary to think about. I guess I need one of those concrete walls and a gun I don't care about to proceed any further.

I do not get it why are you concerned about the round if is a subsonic rd and not way over pressured?

 

[Afalex1]

Because if detenation. Some powders act funny at low charge levels and can turn into a bomb. It doesn't always happen and labs have had trouble duplicating it, but I don't want to risk a kaboom.