I have had the 36grn Varmint Grenade up to 4890fps out of my 22.250 AI with case filling charges of Vit 550.
I was looking for 5000fps but pressure (blown Primers) stopped my quest.
Accuracy was poor, grouping 1.5" @ 100yds, even when i dropped velocities down a more sedate 3900fps accuracy did not improve.
Went back to my old mainstay the 52grn Berger Match Varmint.
I have now had enough of speed and mediocre accuracy so this particular rifle is currently being re-barreled to 22BR.
Ian.