Mayby a fix

I changed my o-ring (reluctntly and crefully with a needle)and cleaned the barrel some more, it did no good. On the Greg Davis site he tells how to make a Crosman barrel shot better. One thing I noticed is that he says the barrels like 5.52 mm (.2173 in)head size pellets. I measured my dicovery hps and found about 1/2 were under that size. I set a micometer to .2173 and seperated the pellets by the ones that would pass through and the ones that would not. I loaded a clip with each size and the bigger ones shot in dime size groups at 35 yards while almost all the under size ones would not hit within 6 inches of each other. I could see the small ones leaving the gun in a spiral toward the target, hittin all over the paper. I have not shot to many yet to be sure if this is the whole problem. The next pellets I order will be 5.52 head size. I can not find an advertised head size for discovorey pellets but JSBs state 5.52 on there pellets.
Jim