[Justinmd]

Firing with a can produces a phenomenon that I've heard called freebore boost. So yes it boosts MV not lowers it. And it's not too consistent in my experience, unfortunately.

A can does increase the amount of blowback through the bore, this raises carrier velocity significantly, surprisingly, by pushing the empty case while still held in the bolt face.

IG, If the increasing numbers means a heavier buffer, and an H3 locked back, I would say that with the H2 buffer your cycle times were too fast for the bolt stop. If you check the rim of an empty case, you would probably notice a part where it looks like the extractor tried to rip the rim off. This will be less with the heavier buffer.