I've just spent an interesting couple of hours cutting a barrel down 30mm at a time to try and get a proper answer to the correct cylinder /barrel ratio for a few different BB weights, and I thought I'd share them here. The test was done with a single gun, using an M100 spring and a cylinder with a 12mm port for a compression distance of 48mm in a 23.8mm bore cylinder. I cut and roughly crowned the barrel by 30mm each time. It was not disassembled from the hop, and neither was the hop setti