The 300 rcm doesn't get over 3000 fps from a Hornady test barrel of unknown length. The last test I saw of one with actually velocity from the 20" tube was in the 2800fps range. The RCM only has a few more grains capacity than the 30-06 and less than the 300 saum and wsm. And good luck reaching anywhere near 300 fps with a rcm handloading. It was very difficult for me to do with a 3000 saum and a 24" tube.
Hornady disagrees, but perhaps you know more about their test results than they do.
