I have the same rifle & I get around .75 groups shooting 210gr Swift Scirocco bullets loaded by Superior Ammunition & around 1-1.25 shooting 225gr Hornady SST's also from Superior Ammunition.
I have grouped the RUM @ 300 yards 1"- 1.25 the win I have only grouped @ 100. A friend of mine shoots them in his RUM H.S PRECISION TAC. rifle & he gets 1/2 MOA to 3/4 MOA out of his out to 700.
I use them for shooting paper & rocks in my 338win & 338rum they shoot great! The win. shoots .75 & the rum .5 to .60 they have a BC of about .870 gun)