I think you are getting the larger groups due to the weight of the bullets you are shooting. Like stated above, the 200grn is optimal and a 240 or 250 is in the range that barrel is twisted for. I have a .460 in a 15" Encore w/break that is the same twist as the XVR.
It shoots lights out with the 200grn Barnes XPB and nothing has walked off after being hit with that all copper hollow point. I have used it on several size white tail deer, pigs from 60 lbs to 250 lbs. I loaned it to a friend that took a cow elk in the 400 lb range.
I shoot a Ultra dot on mine and can't say how it would do past 150 yards because that is as far as I have shot it.
I have never tried cast bullets but they might shoot in my barrel, just don't know.
I know right now is it Heck trying to find factory ammo. I just loaded 50 of the Barnes 200 grain XPB's with H100 powder for this season.
Good luck with your XVR.
1st Photo is the 200grn Barnes XPB next to a 44 Mag XTP
2nd Photo is the 460 with Old red dot I had first.
Mike


You don't quit playing because you get old, You get old because you quit playing.