Looking to SBR a 16s/17s with the FNH OEM barrels assemblies. However after researching, I am seeing alot of different lengths for OAL (on form 1s). Since the ATF form 1 OAL is from stock fully extended to end of barrel correct? Just want to verify/compare #s. Does FNH use rockset on muzzle devices? Why isnt OAL measured with stock folded?