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Excellent idea and there are a few loads posted here and there. As you said there is a stigma attached since its not "our" cartridge. Also there is the lack of bullet selection in .310 and the fact that barrel makers are a little hesitant to make a .308 barrel chambered for 7.62x39 because the first thing that will happen is somebodys gonna shoot hot factory (.310) cheap ammo in it and have problems. The 7.62x39 runs into the larger case capacity problem like the 308 win (though not as bad) with fast burning small kernel powders. Using low charges to get subsonic velocities with the pistol powders usually results in less than 50% full case density (possible secondary detonation) and gives wide velocity spreads. Think of it like this with a small charge in the case setting in the loading block all the powder is resting on the primer. Turn it on its side and the powder is all laying on the side of the case. Turn the cartridge nose down and now all the powder is around the bullet with an air gap between it and the primer. All these will have a different burn and the velocity will vary slightly so you want the case as full of powder as you can get with a small charge. This is where a high volume bulky powder that has a light charge weight is needed. For the 7.62x39 I use to use dupont "bulk" which had a charge weight of 5.5 grains per cc of volume and would make a nice subsonic load without fillers but unfortunately they stopped selling it in the 70's and supplies have dried up. Fortunately Trail Boss came out and it is appears to be an even better substitute since it has a charge weight of 4.6 grains per cc of volume and it really fills a case up. IMR hasn't released burning speed data yet but it is suppose to be close to red dot speed. I have been using it with 200 grain bullets and getting full cases with subsonic velocities (7.62x39) and am getting ready to load some with 125 gr speer tnt's. It is way to fast burning to cycle a gas gun but it looks good so far for bolt guns.
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