Ask the Community

If it is a ring approximately the same diameter as the end of the barrel I believe it is an adapter meant to be used when installing non-Sig branded muzzle devices that require a flat as opposed to tapered shoulder at the end of the muzzle threads. Unless you are removing and swapping out a muzzle device it shouldn't be of any use. That's all assuming that is looks like this: https://www.sigsauer.com/taper-cap-5-56-barrels-1-2-28-thread.html