Not as scientific, but I recently bought a tin of Meisterkugeln 4.50mm 7.0 grain pellets to try. I happened to be doing some rested sighting with my FWB 65, so gave them a go. The spread was just within the 9 ring at 10m which I thought must be down to the variability of my holding the pistol on the rest, but when I tried some 4.49mm R10's, the group was much tighter. Impossible to know whether it was down to the weight variation or the different diameter...
Next time I have the opportunity, I will repeat the experiment with my FWB P34, and maybe try some of the other pellets in my bag.