Fx slug liner .25 chamber?

I an not sure but I cut an FX .22 pellet liner down and put it on one of my pistols. Other than chamfering the edges I did not cut any lead into it, oops I forgot, and it loads and shoots JSB 18.2 pellets in a cloverleaf at 25 yards @ 600-700fps without tuning. Although I think they should have a bit of leade it doesn't seem to make much difference.

Not in the .22 pistol it has an stx pellet liner, not usually slug friendly, and it is not shooting fast enough either. I shoot slugs from my Impact with a.25 slug liner @ 740-980fps and they are nirvana once you have the gun tuned. At 740fps the slugs start to tumble at 150 yards. At 900-980fps I shoot spray-paint cans at 200 yards.

I think giving slugs this smooth bore to accelerate before hitting the rifling probably keeps the overall velocity of the slugs high, and that is why FX did it. The cocking stroke and pellet probe doesn't push a pellet nor slug very far past the brass port and into the liner. Therefore the projectile doesn't get "seated" or started into the rifling until moving fast, and this momentum would be beneficial to keep it moving and accelerating.

I just checked and the lead length up to the rifling on my .30 caliber is the same as your .25. I did change the initial entry angle of the slug liner too because the pellet's skirt was meeting too abrupt an angle from just air pressure and no "help" from the probe. I did it with fine grit wet/dry paper and also polished it as well. It had no ill effects on the slugs.

On another note of interest, I just pushed a measured .300" NSA slug through my slug liner and it was swedged down to .298" once it hit the rifling and moved down the bore.