How do suppressors index on sporter barrels with no thread shoulder?

I am looking at some rifles like the new Thompson Center Compass and I see that while the muzzle appears to be set up to have a suppressor index on the muzzle it self I am wondering since the manual says nothing at all about suppressor mounting safety what happens when one mounts a can with out a step in the thread adaptor. I figure the adaptor should be hitting a shoulder of some sort to index.

I am about to have some muzzles threaded on some hunting rifles and I don't really want to have custom end caps made for each diameter so that they will index off the muzzle. Is there a third way to get a good index beside the muzzle or a step behind the threads? I can't imagine I'm the first to ask this but there is no info on the internet anywhere I can find.

I think this is usually done by threading 1/2 X 28 and then an adapter with a shoulder in the appropriate thread size for the suppressor or mount is rock set onto that. At least that's what I've been told by a few different guys.

So what about for those which don't index on the muzzle. That's the issue I am running into.

I thinking indexing on a shoulder is a hold over from back in the day when a lot more barrel threads were shady.
Yes, I understand that a squared shoulder that the suppressor can snug up to can be optimal, but is isn't always
a necessity if the threads are concentric and within spec for the required pitch.  

My HK91 has a slim profiled barrel with run-out threads and my suppressor screws on tight, and concentric with no shoulder.

Assuming all parts are within spec, and tolerance creep is at a minimum, you may be fine. Only way to tell is mount and check.

Also, as a side note, if the barrel, mount, or suppressor threads are crap, mounting another device like a QD mount etc isn't going to fix anything, with or without a shoulder.

Just to clarify, this is a barrel threaded about 1" or so, with a collar threaded on to the rear portion that creates the shoulder -correct?
Nice work.

Thanks for the help greenm4guy. Another solution I came up with is a possibility would be to have an adapter made for the suppressor that would allow me  to use silencerco''s harvester end caps.