I think most people who shoot Piston, shoot what they get on best... as said, there's recoiless piston rifles allowed in the class, but I don't think we've seen any this year.
Off the top of my head Duckhunter, Jamesy and JamesO, Mark Fisher are shooting or have shot springers this year... Nick Murphy is the champion, and will have no doubt fettled his prosport to make it what he wants, and i'm sure the others have tweaked but tuning only really adds smoothness and sharpness to the rig and perhaps makes the recoil a little nicer, but in the equation of you and the rifle and the skills needed for FT, it's a small % detail.
Common rifles at the moment are the 97/77's, tx200's and prosports. SR's and whizzers do make an appearance now and then, but for a while, the 'recoiless' rifles haven't been seen that much.
In the right hands, they're just as capable as PCP's...
I'll probably be using a 97k in the winter league... that's been vmach'd.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep