I did not find the suppressor to be “kind” to my 416 Shorty Uppers until I placed HK OEM vented 10.4” gas blocks on them and had the barrel gas ports tuned to them. They shoot wonderfully now unsuppressed and suppressed with my SB2.
So I’m not sure about SFs new description claim that it helps with certain piston guns that do not have adjustable gas systems. But yes it’s always been designed for SBRs of lesser length than the M4 (14.5”) or <10”
If I am not mistaken the RC was designed to operate with the 416 and the SB2 came after with the SOCOM2 line of suppressors to cater to <10” barrel lengths and frangible ammo (as they used to state).
Do you have an RC or an RC2? I believe the only difference is Hand VS Machine welding.