I've got the same thing - Triple-X in 1/2-28. The baffle openings are actually large enough to shoot 9mm through... just barely. But I think I'm just grazing a baffle somewhere, as I get severe POI shifts - more than you would expect from just the weight of the can. I expect yours is bored the same. (This is the standard .223 can. The cans that were overbored to actually use with 9mm are opened up even bigger.) So figuring a perfect fit for a 9mm, that still gives you .047" tolerance to play with. That's a pretty big number, and an adapter would have to be pretty badly out of round / off centered to get to to where you had trouble with it. I wouldn't have any issue using this can with an adapter on a semi-auto .308. (full-auto .308 might be okay, but you'd want to make sure the can stayed on there pretty tight. Depending on what .308 you have, it might be better to get a spare barrel threaded 1/2-28).
I'd call Mark at
TROS about an adapter.
Or, better yet just give Mike Klos (the guy who built your can) a call or stop by, depending on where you are in MO. I'm sure he could build an adapter as well. If you're on the STL side of the state, you could probably have him make an adapter, and then you stop by the shop and have him check with the can & gun for runout.
That's one of those things I keep thinking about having done. I just haven't yet. I'm thinking the can would go well on my .300 Whisper upper. I had the Contender .300 Whisper and the bolt-action .243 threaded 1/2-28 so I could use it as-is on those.