I have two 300 ultramags and use the 180gr tsx in both.I use 88gr of r-25 in one rifle and 93gr of r-25 in the other rifle.One rifle produces 3360fps and the other 3380fps.The difference in powder charge seems large for such similar velocities but I m using different lot#s of powder for each and the barrels and throat lengths are different as well.In both cases the col is 3.670" and the primers are fed-215.