You'll need a much higher velocity. From what I've learned here, as well as having read as much s I can find, it's much easier to go down in bullet weight and back the velocity off than the go up and try to match the regulation.

Somebody here, Capt Curl? Had awful trouble with a 9.3x74R when they used 286Gr bullets in a rifle regulated for 255s. He just couldn't be them squirting out of the barrel fast enough to stay together at the target.

Best of luck and let us know how you go!