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The issue with coming up with an adapter for a sound suppressor is maintaining concentricity with the bore well enough to prevent baffle strikes within the suppressor.

Do your Colt 6920 and S&W 15-22 not have a muzzle device (flash suppressor) on them already? If so, they are likely affixed via threads and possibly also pinned if the barrel length is less than 16". If these barrels are bare and don't have muzzle devices on them, it may be time to get them threaded or source new uppers with threaded barrels. I presume that an adapter that fits over the muzzle end of the barrel could be engineered, but some mechanism to ensure proper alignment with the bore is required.

The answer for the Glock is an aftermarket drop-in barrel with threads. I can't really think of a way that an adapter would work in this case since the muzzle end of the barrel fits fairly closely within the front of the slide.