I shot bp quite a bit in my Mk.VI. It worked very well with a regular flat point bullet intended for the .45 Colt. I only used the longer Mk.I brass, though. Clean up in the break open Webley is a snap! Just be careful that fouling hasn't built up under the cylinder retainer on Mk.III and later revolvers. It should be noted, BP should be the ONLY powder used in old Webley's that lack the dovetailed in, hardened breech plate.