At one time a gun club in Washington state had matches for the XP-100 and groups would make anyone drool. However most, if not all were highly 'smithed. Not too sure but think the record was in the .2's or .3's at 200 yards. Watched a shooter at a local club shooting at 200 yards, three shot groups, none went over 1". This was a stock XP-100!

Out of a rifle, when you can honestly and easily get 3500+fps out of a 40gr in a 221 (using AA1680 or LiLGun), its efficiency is amazing.
Remington offers at least two rifles in the Fireball now, and for the bigger $$, you can get a Cooper.
Great round!