I have two 338RCM M77 rifles. One is the 20" RCM rifle now in a McMillian classic stock. I also built a 22" version with Rock Creek #3, also in a McMillian classic. While carrying the 20" is really nice, I find the extra weight out from of the 22" makes for a steadier hold.
I have shot one moose with the short one and three with the longer one ( the last just two weeks in Newfoundland) and have to say its about my idea of a perfect moose cartridge. I hunt the east so we don't have mean bears, so I haven't felt the need to shoot heavies. Instead I have used 185TTSX, 210NP and 210TTSX. I did catch one of the 185s so have settled on the 210's although at 338RCM velocities a lot of bullets would undoubtedly do fine.
I am mostly a carry hot kind of guy, but my NF guide had me carry cold and It was the first time that three down felt a little light. Maybe the fact that the other guy in camp used a magazine full of ammo to put his moose down helped with that perception. In the end it only took one shot for my moose.
In any case I am happy Mainer mentioned turning the follower around to get 4 down in the Ruger I am going to test that out as soon as I make a few dummy rounds. I also have a M77 in 300WSM that might also benefit from the follower trick.