Subsonic 7.62x39

T

the young gun

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Hello, does anyone here know of any commercial subsonic 7.62x39 ammo? Or anyone have any experience tinkering with any sub sonic hand loads?

Only thing I could find online was that EBR Jackhammer stuff using a 220 gr projectile. Not realistic I will get to see it in Canada.
 
It is easy to make. Load a heavy 312 bullet (like 180gr) and a suitable powder. I use 2400.

There is a quite a variation in velocity between rifle. My rifle might need 10 gr whereas yours only needs 7 gr. You want ammo to be about 1000 fps.
 
A word of caution about subsonic rifle loads. There are documented cases of catastrophic failures due to a "detonation"-like phenomenon when there is significant air space in the cartridge case. It is best to use powders that maximize volume to avoid this condition. Trail Boss seems to be the preferred powder these days as it's very voluminous. If you're experimenting with pistol powders in low charge weights you should drill out the flash hole to a larger diameter to facilitate better ignition, and consider using an inert filler to take up the rest of the case capacity. Once drilled though NEVER use these cases for full power loads! Mark them in some fashion.

You can use bullets intended for the .303 British as they mic out to around the same diameter, .310-.313. The bullet weights are also much heavier than what you'll find for 7.62x39 which is typically in the 110-150gr range. Lapua also makes a dedicated 7.62x39 subsonic bullet but you can imagine what those will cost. Another option is to cast, especially if you plan to hunt with the load. Bear in mind most jacketed bullets will not expand properly at these velocities.

Here's a site with some load data: http://members.shaw.ca/cronhelm/762Page.html
 
As I was saying. Use a suitable powder. 2400 is the most commonly used for sub sonic ammo made for canned rifles. No need to use a filler with fast powder.

DO NOT drill out the flash hole. This reduces ignition. Ignition is best with the smallest possible flash hole. One reason why Berdan ammo has very good SD.

A round nosed bullet (cast or jacketed) is usully the most accurate. I have used 180gr and 215 gr round nosed bullets intended for the 303Br. The bullet will be deep in the case and use up most of the excess powder room.

Load development is best done with a chronograph, so you can see the velocity. Failing that, an observer to the side can tell when the ammo goes subsonic. Start high and work down. Load in 0.5 gr increments. For your first test, 1 of each will suffice.

Once you have an idea of the correct powder charge for your rifle, make some test batches in 0.5 gr increments to see what is accurate and what load consistently stays quiet. Test the loads of 900 to 1000 fps. If the rifle is not canned, a listener to the side is helpful.
 
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I know your background Ganderite and I respect that, however I was simply passing along what I'd read from others who have experimented with this. No need to be snooty about it.
 
AK said:
A word of caution about subsonic rifle loads. There are documented cases of catastrophic failures due to a "detonation"-like phenomenon when there is significant air space in the cartridge case.
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Fill it up the case with "cream of wheat" original. Also gives your ammo a nice "toasty" smell after firing.
 
The OP was asking about sub-sonic in 7.62x39.

That is a small case. After seating a 180 gr bullet deep, there is no empty case volume to fill with cream of wheat, or anything else. In fact, using 2400, some loads are compressed.
 
Good info. I suppose there's really no set way around it but to develop a "perfect" load. Only curious for no reason in particular, more so curious as to how they can be tweaked to work a gas gun with any efficiency. I'm thinking the bullet weight is going to make or break it.

Thanks.
 
Ganderite said:
As I was saying. Use a suitable powder. 2400 is the most commonly used for sub sonic ammo made for canned rifles. No need to use a filler with fast powder.

DO NOT drill out the flash hole. This reduces ignition. Ignition is best with the smallest possible flash hole. One reason why Berdan ammo has very good SD.

A round nosed bullet (cast or jacketed) is usully the most accurate. I have used 180gr and 215 gr round nosed bullets intended for the 303Br. The bullet will be deep in the case and use up most of the excess powder room.

Load development is best done with a chronograph, so you can see the velocity. Failing that, an observer to the side can tell when the ammo goes subsonic. Start high and work down. Load in 0.5 gr increments. For your first test, 1 of each will suffice.

Once you have an idea of the correct powder charge for your rifle, make some test batches in 0.5 gr increments to see what is accurate and what load consistently stays quiet. Test the loads of 900 to 1000 fps. If the rifle is not canned, a listener to the side is helpful.
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Curious, with a fast low weight powder like 2400 in a small case like the 7.62x39mm, why do you suggest 0.5 grain increments? Isn't that a little corse?

I'd generally agree with you on the use of round nose bullets, however, that isn't always the case. Hornady .308" 220gr. RN bullets are generally poor at subsonic velocities. Guys shooting .300 Blackout report extremely poor results. My experiences with that bullet are similar. Perhaps, it's the balance of the bullet and it's center of gravity that makes it a poor choice at subsonic velocities? I dunno. I just know it doesn't work well.

There's a really good .311" 247gr. cast bullet mold available in the US that was designed with subsonic use in mind and would be ideal for .300 Blackout and possibly 7.62x39mm. Some have reported good results in 1:10" twist barrels. I have this mold for well over a year but haven't gotten around to doing any casting yet. Most of my shooting has been done with jacketed bullets.

Here's another thread on toying with the 7.62x39mm. It's an interesting read as well. http://w ww.quarterbore.net/forums/showthread.php?t=9381

the young gun said:
Good info. I suppose there's really no set way around it but to develop a "perfect" load. Only curious for no reason in particular, more so curious as to how they can be tweaked to work a gas gun with any efficiency. I'm thinking the bullet weight is going to make or break it.

Thanks.
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Subsonic gas gun applications with 7.62x39mm are going to be very challenging to say the least if you expect it to cycle. Depending on which rifle you're using and a myriad of other variables to long to list here, it might not be practical at all. If you don't care about cycling, you're far better off with a bolt gun or break action in that cartridge.
 
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I just recalled something else i used to do. For 308 cal rifles, i used .312 bullets. The extra diameter boosted pressures and helped burning uniformity. Another variable to play with. I used the 312 hornady 174 gr RN bullet.
 
2bad4u2 said:
Subsonic gas gun applications with 7.62x39mm are going to be very challenging to say the least if you expect it to cycle. Depending on which rifle you're using and a myriad of other variables to long to list here, it might not be practical at all. If you don't care about cycling, you're far better off with a bolt gun or break action in that cartridge.
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Agreed. I was tinkering with the idea of trying to make a cz 858 function with subsonic loads. However, even with considerable trial and error of altering the gas port, the springs and load development, I'm expecting over/under gassing issues, I'm expecting to have to #### around with the springs to the point where I'll have to order 4 or 5 and throw close to that many away. I was also considering the thought of reducing the size of the gas port, combined with making the upper and lower hand guards around the gas port a "sealed" unit to try and improve the efficiency of the gas on the piston in hopes of being able to make the gun run with essentially less gas generated from lighter loads. I think it would take a combination of gas port work, spring work as well as some back pressure from a can to make it run, if it is possible. Either way, I'm going to do some more digging and try and compile a list of mods to do to try and make one run. Before I get started I'll post the list and get some more input.
 
"Curious, with a fast low weight powder like 2400 in a small case like the 7.62x39mm, why do you suggest 0.5 grain increments? Isn't that a little coarse?"

Yes, but the object is to quickly find the powder charge for 950 to 1000 fps. If you have no data to start with, big steps will quickly get you into the ball park.

To make a semi work subsonicly, you need low chamber pressure and high port pressure. It is obvious that a fast powder would do the opposite, so that suggests the reverse is what you must use. As you try slower powders, you find they burn erratically at lower pressures, so it is hard to stay sub sonic for all shots and accuracy is poor.

the slowest powder that works well at low pressure is 2400, which is why i suggested it in the first place.

Try some 180 gr 303 bullets with 7 gr of 2400, and go from there. It would be great if it was subsonic and ran the action, without modification.
 
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