after measuring the pellet skirt of top quality JSB reds in 4.52 skirt I have detected 4.569mm to 4.513mm and the 5.10gram mass from 5.07 to 5.18 gram, I think that is more likely to give bad grouping at 45 yards+ than any barrel issue, wash, weigh and size every pellet if you plan on trying to put them through a keyhole over 25 yards.