My theory is the flexing of the thin receiver walls which absorb the shock of the discharge, due to the rear lockup (which is beefy as heck but something has to give). Endemic to one degree or another with all rear lockup systems I think. Just a theory, I could be wrong.
I was thinking on this..
Front locking bolts transfer the energy to the receiver quickly via the lugs at the front of the bolt. But this transfer "pushes" back on the rest of the receiver.
Rear locking bolts transfer the energy to the rear of the receiver, which then "pulls" the rest of the receiver rearward.
So I'm not sure at the receiver level there's much difference?
Just thinking..
