[LouBoyd]

Aussie26, you didn't mention the length and twist of your barrel or the type of action. Without that its just guessing. It would also be good to know what sort of performanc you want to give an idea if it's practical at all.

I've run computer simulations (Quickload) to see what might work for my DPMS LR-338L. It has an 18" x 9" twist barrel. I didn't come up with anything which I think would come close to cycling the action without extensive modification of the the gas system including moving the location of the gas port. Like the 308, there's just way to much chamber volume to be a good subsonic round. If that barrel were on a bolt action there would be better choices.

If you just want subsoinic reduced loads for just about any bolt action cartrige there are two methods to explore. One is shooting lubricated cast lead bullets. They usually have decent accuracy to a couple of hundred yards. Without knowing a specific barrel length and bullet I can't suggest a load.

Another way is to make reduced volume cases by "filling and drilling" the case with solder or epoxy reduce the chamber volume to something reasonable. The Federal 338 had 57.5 grains case capacity. The 338 Specter, a cartridge known to perform well subsonic with 250 grain jacketed bullets has 28.8.