I have a Winchester model 255 22 magnum in lever action I just picked up and a friend has what he calls a 22 magnum but his reads a 22 W M R. I was reading one of the forums that someone was having problems with only getting a 10" group and it was said he had the wrong ammo, and that there was a difference in 22 W M R & 22 MAG. Can someone tell me the diff. I can't find anything where I'm looking.