I am considering picking up a 338 suppressor. I would love some subsonic rounds to shoot through it so I get the most out of it. I was thinking of using trailboss do to its bulkiness. Also I have a 1-10" barrel, is that going to be fast enough to turn 300 matchkings going that slow or is 250 probaly going to be the max.

I reload 338 RUM, and with that huge case capacity I think you are going to have too much velocity variation to get much accuracy when you dabble around in the subsonic realm.

You can do things like make up cases with a smaller internal volume and stuff, but if you do all that work it will be simpler, and maybe even marginally cheaper, to just build up a different rifle based on a case more suitable to subsonic velocities.

Now, if you are dead set in using what you have, they use a 1:8 twist for 220 gr 308 bullets so a 1:10 twist may work OK.

I have seen subsonic 338 laupa factory loads before and the laupa has several more grains of h2o capasity. I just figured it was possible to achive the same with the rum case. If worst come to worst I may build a 338 federal with a 1-8 polygonal pacnor barrel.

thanks
skog