My SLP is the Mark1 model, which sports a 22" barrel and longer magazine.
I can shoot reduced recoil 7/8 ounce slugs through it using the light piston. Using the heavy piston, I can reliably cycle 1 1/8 oz. Federal bird shot, although you can tell it would rather use the light piston. I routinely practice with 1 oz. Federal Truball reduced recoil slugs and also use them at training. They will cycle either piston but after multiple days with no maintenance, the heavy piston will let you know its time to clean up or simply use the light piston. The light piston is rated for loads less than 1.5 oz. so it is not an issue to use it with the slugs and buckshot loads I run.
