I noticed the SIG OEM threaded barrels for P320 have a slightly different profile than regular threaded barrels. Sig barrels have a distal region after the threads. Can I still use a regular piston on them or should I go with one that indexes off the muzzle. For reference, Ill be using the Sig Mod X 9 suppressor

I’ve had better luck with pistons that index off the muzzle than the shoulder on my P320. The standard 1/2-28 piston that came with my Obsidian 9 “works” with my P320, but it walks off very easily. There’s just not enough of a shoulder on Sig’s threaded barrels to make good contact with the piston.

The Sig pistons should be good to go with your factory 320 barrel, and I believe they do index on the muzzle face due to the unconventional threaded muzzle profile they chose for their 320 barrel. If you ever go to run another can on that factory Sig barrel, you need to make sure the piston has a bulkhead in the distal end of the socket for muzzle indexing, and that the counterbore in the very rear of the piston before the threads start is large enough to accommodate the barrel diameter behind the threads. Prior to the Mojave 9 pistons going into full production, I had to open up the counterbore a few thousandths of an inch to take the factory 320 barrel and prevent the barrel diameter behind the threads from touching the piston and providing a false sense of seating on the muzzle face.

SilentMike
Dead Air
AAC 1998-2018

So the Sig pistons should work fine on Sig barrels and other barrels with similar profiles like glock threaded barrels, or really any other hosts since the sig piston indexes off the muzzle?