Duplex loads?

[shooter93]

Here's the scenario....A friend has a gas piston AR in 7.62x39 shooting a 200 grain lead bullet. He wants to be able to shoot it sub sonic....1050 fps and still cycle the action by adjusting the gas piston. So far fast powders won't cycle it....too little gas. So....he needs a slower powder, some he has tried shoot to fast, that either fills the case and cycles the action or perhaps a duplex load....any suggestions? I have messed very little with duplex loads but I know some people have used them with success. Thanks.

[felix]

Your scenario is correct. Your solution is also correct, except you have to have a certain amount of gas at the right time as you know. A duplex load will not deliver, unless the amount of TOTAL powder can produce the amount of gas needed. So, that means the faster powder should not be too much slower than the slow one. This is an interesting challenge without changing the gas port size or location. ... felix

[shooter93]

He can adjust the gas port but not it's location at this point. We have been experimenting with a few different powders just haven't found the right one if it's even possible. maybe I'll get lucky and get a suggestion here. have any thoughts on the slowest powder usable Felix?

[felix]

That's hard to say, Shooter. I'd try a case full of H414, no compression, and see how close that comes. It might be too dirty and still too much velocity, however. If it is too dirty for the number of shots taken, then no slower powder is going to work without a kicker. ... felix

[Bloodman14]

Maybe use magnum primers? Honestly, I have no clue about this subject.

[303Guy]

Lil'Gun has some weired characteristics but might not work with the case volume/sectional density/expansion ratio of the 7.62x39.

[Harter66]

I've been working w/some 200 gr boolits in paper patches for my sks. Although subsonic was not my goal I have had some success w/4350 IMR. The loads are held to less than 25gr to get a magazine usable length w/my boolit. Below 23gr I have a lot of unburned powder. My rifle is also spacious in regards to its chamber and throat dia. My next trial will w/a change in powders will be toward a slower powder 4831 maybe. 4895 was too fast. W/a tighter chamber and a proper bore you might do better. My bore is 305-316.