Quote Originally Posted by TonyL View Post
Quite a few variables here. You don't mention preload. At first, looking at the combined weight of the piston and its weight, one might be tempted to try it without the weight. But if we're running very little preload, the increased piston weight will help counteract bounce, bearing in mind the larger diameter piston's surface area. One might be tempted, if you have to play, to open the TP out to 3mm and use a spring with thinner wire but more preload? Losing that piston weight then might quicken the action up?
Pretty much on the ball, Tony.

It's a Lightning, I think. I'd replace the piston weight with a replica turned from acetal, fit a much softer spring with preload to compensate, turn an acetal guide to suit the spring, and look for circa 10 ft. lb. with the most efficient pellet.

I think I'd leave the transfer port as is. With such a short barrel, you want the mass air flow to choke earlier in the stroke.