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Yes it's still any barrel you like as long as it's 5.56 and 16.5 long.

Yes it all makes for a different recoil experience. The weirdest was the G3 I remember it had an odd recoil pulse but that's probably something to do with the roller locking system.

Whats the recoil impulse like? With 223 piston rifles, the parts moving can be more noticeable than with 308.

C-Cat length :D