Well, it may have something to do with the back pressure from the can. I have never run subs without the can so I don't know if they will work that way. Any of the 920 FPS stuff works fine with my Mask.John,
Thank you for your replay. My Ruger 10/22 is 16.5". My CZ 452 is 22", the Ruger MK IV target is 5.5" barrel.
I thought sub-sonic ammo wouldn't cycle a semi-auto?