for my pistols i use jsb 4.50 (yellow tin) rifle pellets.
slightly heavier than the pistol pellets and better for 20yd or 25m disciplines; so i am told by the steyr technician.
if the pellet falls through the barrell try the next size up.
to be honest i would chose h&n finale match, but the jsb's are much cheaper and i am not good enough to notice the difference!
bench tested jsb's at 20yd and 10 out of 10 pellets all went through the same ragged hole. good enough for me .
try not to get caught up in the pellet testing trap!
stick to a good make and practise.