Rifling Engaged At Loading REAL. No need to re-size. I shoot them out of a number of rifles with various bore sizes. The main thing with a REAL is, don't push them hard. I find when I get around 70 grains that is a the sweet area with them. No more, but less is fine. The lube in the grooves is important. It helps them slide down the bore and to seal the bore ... powder to bullet.