If you have an hour or two spare (and haven't already) there's a couple of 'vintage airgun' gallery websites that have a few rifles like the Wray (small run/ custom builds) that are worth checking out
Yes had the concept action up and running, efficiency was in the late 50's with a light spring and minimum recoil. It came about after daydreaming about transfer port dimensions (I'm sad like that)....
View attachment 531155 Basically, the Crosman barrel is fixed at the muzzle end, and floating at the breech/ probe end, and can be adjusted in or out to open or restrict the port. The barrel is held central by the piston as it traveks down the comp tube. The probe would load a pellet into the leade (same as a pcp) but retract and cam back slighlty when locked to allow for flow.
A pellet receives the majority of its energy from the compressed air whilst the piston is still moving. You need a transfer port of course to act as a restriction to allow pressure to build at all, but that restriction also prevents flow so.....I wanted to see how wide/ short you could go (and in this concept you can 'sort of' go 8mm wide (the diameter of the Crosman barrel) by as little as 0.1mm, upwards, in length.
Ultimately this was just about testing the compression tube/ barrel/ TP arrangement. I made a basic trigger release, and cocking sled using chain and an underlever from a 77 (piston latches at front end and cocks from rear)....
View attachment 531151 .....but they could never really be used in a full working model. One day though, when life is different, I'll design a chassis/ proper trigger arrangement, and take this further......