@ECVMatt - what is the buffer weight you’re using in any of your carbine stocked rifles?
Most civilian AR’s with carbine buffer systems will have grossly underweighted Carbine buffers at only 2.9oz, whereas a Rifle buffer is 5.2oz. Kick in an H3 or Vltor A5H2 buffer at 5.3-5.4oz, and the difference in recoil impulse for the same upper on a carbine vs. rifle lower almost completely evaporates. The bigger trouble happens when folks have a grossly oversized port (intentional by barrel makers to ensure function) but then run a lightweight carbine buffer - these run, obviously, but they beat the hell out of themselves, just to avoid immediate customer service calls.