I swapped out the standard buffer and spring on my AR with a JP Enterprises Silent Capture system with the lightest spring. The rifle now cycles fine including last round bolt hold open with my subsonic loads (220gr SMK over 9.0gr of Hodgdon Lil Gun) instead of being a single shot. The JP system eliminates the buffer/spring noise, very fun suppressed. The sub loads are dirty though, makes me want a piston system. I'm tempted to spend the $200 to get the ATF tax stamp so I can run the short barrel (I would get the 8.5").