Why not get a barrel in 300 Norma Magnum for your Blaser. It comes in 1-9 twist plenty enough to stabilize the heaviest 30 cal. bullets like 245gr. Berger Hybrid Hunter and everything lighter. Norma and Lapua brass available. Use Lapua if you go that route, Norma is soft. I personally have Blaser R8 in 300 Norma Mag semi weight barrel. You as a Blaser owner know what that means as a barrel contour and weight. It is absolute hammer and pleasant to shoot. Very accurate. The downside is that it is relatively heavy, and you have to thread the barrel if you want to install some sort of muzzle device because for some reason Blaser decided not to sell factory threaded barrels in USA except the heavy contour "Match" barrels. You will need an appropriate bolt head too if you don't have one already. There is plenty of room in the magazine, that you can sit the bullets close to the lands and even jam them if you wish.
You can practice extensively with the same gun if you already have a barrel in appropriate caliber for target shooting. If not buy one. To be able to practice with the same gun you gonna hunt with, will do more for your shooting success rate than anything else. That is the beauty of the Blaser system. I personaly will never go back to traditional rifles for hunting.
Good luck with your sheep hunt!