actually quite good. i use them because they seem to seal better than the metal breech (you can tighten them till they squish the transfer port shut...) i can say the average 2240 stock will give 1 inch at 10 yards no problem. most do better than that. Even with the Gamo ammo ( mine likes the gamo wadcutters...) try this. loosen the transfer port allen a bit (so its a little wiggly, but not off all the way). then loosen the barrel band. now lined the barrel as straight into the plastic breach as you can. tighten the transfer port using the long end of the allen and using the short to torque it. then thighten the top and then the bottom barrel band set screw. the bottom one not too tight, or you'll have a hard time opening the powerlet cap. try again. if you do not get groups, take the barrel off, knock your front sight off and check your crown. that should do it...