Couldn't one use a jam nut?
No, Yonderprick says that'd be all F'd up. But, if you got alignment, then WTF not ehh? Recall he suggests having adapters custom made to shoulder on the muzzle. Yah, that's the ticket.
But, my question posed today is solely for discussion as the proper solution has been offered many times, thread 1/2-28" and use a good enough adapter. Then no whining is required.
What is this magic alignment that just happens without a shoulder? There is so much you don't understand about this, your ideas just make everyone dumber for hearing them. You already said your own suppressor threads up to a shoulder, but you're insisting it doesn't need it? Why don't you have that shoulder removed and see how it works? LOL
I only suggested an adapter to shoulder on the muzzle for cases where a barrel is too thin for an external shoulder. There has to be a shoulder (either square or tapered) in the system one way or another.
Whackem - a jam nut can be OK for a brake but generally isn't adequate for suppressor alignment. It can be done if the jam nut is fairly long, like 1.5-2x thread diameter, to avoid canting. The collars on Gtscotty's rifles in the pics above work in a similar way; they are long enough to hold square on the threads. Difference with those of course is they are probably loctited to the barrel and then the shoulder trued in the lathe after installation.