I've been shooting my 338RCM since last spring, and it is a great little cartridge.
I've settled on RL15 as my powder of choice and hornady 200 gr SST. Keep your loads reasonable, it is a very accurate cartridge.
The only othe bullet I've tried is some old 180 grain ballistic tips again with RL15.
My rifle is just a little hard to hang onto on the bench but groups under an inch are no problem.
I think if more people tried it they would be surprised. I just wish Remington would put it in thier model 7.