I believe that cap has a 1/4" hex socket in it. They can be tough to get them off the first time but a bit of heat will help. If that's the problem, removing the cap and shroud, then firing the rifle to see how the groups look may reveal it's not the cap, but the crown that's the problem. If it's the cap, you can get a .25 cap from Crosman, and it will fit the barrel and shroud, but it has a larger dia. socket(3/8") to accommodate the larger round. Thanks, Unk...that's much easier solution than what I was thinking of trying. However... I believe I may have found my problem. The pellets I was using when I first noticed this clipping, were some Daisy wadcutters. This morning I tried some JSBs,CPHPs and RWS Super Domes...no clipping with any of those.Then I tried the Daisys. I'm thinking they were the culprit all along. I blacked out the area on the cap with a marking pen before shooting and saw no bright spots with any except after shooting couple of the Daisys. I had found these pellets at a garage sale ( about a quarter-tin) and the guy gave 'em to me. I suspect the ones I fired were defective so I won't be shooting the rest of them. Thanks, guys.. Larrypv