This isn't really scientific but it's sort of related to your comment/question about BC being better in a springer as opposed to a pcp ...
I used to pop down to Rough Wedge on Sundays in the Winter if nowt else on ( there is a more local club to me now that shoots HFT ).
Sitting on the plinking/zero range one morning there was a knock down/up target ( I think about 30 yards ). The paddle was a bit stiff/dodgy and people couldn't reset it. I shot it with the 77 and it reset every time. I was using the same pellets ( AA Field 4.52 ) as a number of pcp shooters but non of them could reset it when hitting the reset paddle. We tried with them hitting it at the top and bottom of the reset paddle and me hitting it top and bottom. The pcps wouldn't reset it but the 77 did.
This led to the pcp guys claiming the 77 must be well over the limit. The chrono was out so we tested the guns. The 77 was doing the same as the pcps ... about 780fps ( @ 1 foot from muzzle ).
I guessed at a conclusion that the pellet deformation out of the springer was different and that must have been causing the pellets to hit the paddle with a different force ( I've seen the pics in the Cardew book where the pellets look different fired from a pcp and a springer ).
Maybe the springer pellets were holding on to more speed at 30 yards ( higher BC )?