Okay Buggman - As I said earlier, the choice is limited for barrel recoil and airsoft. But, with a few mods it is possible. I expect to have to machine the inner barrel down and maybe open up the outer barrel to achieve a sliding action that can be operated via a servo and pull rod. I would love to do the challenger but that has a really narrow gun barrel and looks a non-starter. Might have a look at the Leo and the Abrams though. I'll finish the M41 first and then look at the KT. Too many tanks - not enough time!!!! darn it.

cheers

CaptB