Each airgun seems to be different in terms of the pellet it shoots most accurately. Then there are other variables involved that affect accuracy like the condition of the barrel leade and crown and the position of the barrel band or bands...
Barrel Band position? You think so?? My Disco used to shoot Gamo rockets super well until I disassembled it. I have a BNM breech no shroud and TWO barrel bands. Then those stopped grouping well and it started liking Polymag shorts. I took it all apart and did some work again and now it loves the Gamo rockets again! I hope it stays this way for good because the Rockets IMO are the hardest hitting pellets. I wonder if its the position of my barrel bands??