Holy cow
Is that a hydraulic recoil buffer (forgive me if I have the term wrong)?
Nice group indeed. What are you tossing with that? Civil war repro cannon I've been assisting shooting the past two years at one of our club's annual functions, also gets pretty impressive groups (but nowhere near that close) provided the loads are kept very consistent. We can keep them all on the fender of our target van anyway if we're careful. The owner uses cement in the small pepsi cans.
Beauty, thanks for posting