An easy way to determine rate of twist is to put a tight patch down the bore and slowly draw it out and see how far it takes the rod to make 1 revolution (or a half of revolution x2). The PRB should work well for 1:48 or slower twist rate. A twist of 1:48 or faster conicals would probably shoot better. There are so many conicals out there that you will need to experiment and see what ones shoot the best. Out of my 1:48 and 1:28 twist barrels I get good results with the 250 gr REAL bullet and or the 275 T/CMaxihunters. One of my 1:48 barrels shoots a PRB better than anything else I've shot out of it. I'm getting to the point where I have to keep a log of what shoots best out of what rifle. And my ammo cabinet shelf where I keep my ML bullets looks like a shelf from Cabela's.