None available currently but you can backorder them:
I shoot the 200s in 300 BLK - they're designed to open slow, and these two are in your twist range. Hornady 190gn Sub-Xs are ok, you can also use the 160gn FTX for the 30-30. Some people have been pulling the polymer tips from Hornady bullets (especially in the big 458s) to get better expansion. If you did that I would drill the cavity more open.
My opinion (I'll only give it once, promise) is that you're beating a square peg into a round hole, centering mainly around a 26" 10 twist barrel isn't right for this. The 308 can be made to work but the twist is going to hurt you a lot by limiting your bullet weight/length. No way you're going to get there with a 200+gn mono, which are the ones that expand the best in my experience.
If you want to do this though (I'll support it, I'm crazy when it comes to subs), start high, work slower, make sure you don't stick a bullet in the barrel, and make sure bullets are stabilizing before you launch your can downrange.
One issue you'll be working against is the extra case capacity of the 308 relative to the very small capacity of the 300 BLK (I use that a comparison because it's a versatile 30 cal sub). Bullet weight isn't just about retained energy, it's also about being able to use a larger charge weight yet stay slower and because bigger bullets take up more space, both working to maximize your load density. Seat as deep as you can, this isn't the place to seat all snuggly with the lands. You can try to edge up into 180-200gn bullets if they're cup and core, preferably flat base, but shoot enough without the can on to be sure you won't get a baffle strike. This is a big reason I have a Hybrid 46 from SiCo - the larger holes in the baffles give a lot more margin for error when I'm doing sketchy things.
This link is an interesting read where he goes over using pistol powders in the 308 specifically - those powders might be easier to come by than the cowboy powders.
Just got my supressor looking for loads for subsonic - pretty well skilled on hand loads bought some (hate to do that) Corbon 185 gr - very cool seems like everyone says use Trailboss powder never used it thanks in advance Rick
www.snipershide.com
I have NOT tried his shtick about magnum primers and drilling that flash holes on the cases out, I won't vouch for that all nor recommend it until you've loaded a lot of subs. I use magnum primers, but drilling out the flash holes seems like a poor solution to the problem of trying a different powder. Natchez has H110 in stock now, Precision Reloading has IMR 4227, and it seems like pistol and shotgun powders pop up pretty frequently.
Looks like the general wisdom on Tin Star is start at 12.0gn and work down from there. I'd be curious to know what the full case capacity of TS is - fill up an entire case with the powder and weigh it, and see how 70% of that compares to 12gn.
One last thing to leave you with - don't assume velocity will fall in a linear manner, it can drop off very suddenly.... I recorded a 190gn Hornady Sub-X going 614 FPS from a 300 BLK rifle while working down. You'd better believe I checked the bore even after hearing the bullet skip off the ground and hit the backstop. The load dropped from the edge of supersonic to 614 FPS in just over a grain of powder - a 10% load reduction cut velocity by half. This wasn't a poorly charged case - I was intentionally working down ladders with several powders, and that one went south very fast.
