i would recommend agains shooting cast bullets in any of the semi auto tactical guns. You probably won't have a problem if you just plink a little but if you use the gun the way it was meant to be used you will have lead build up issues. The 300 won't be as bad but then again if you do want to use it the way it was designed that's alot more expensive way to go than the 5.56

I won't be wronged. I won't be insulted. I won't be laid a-hand on. I don't do these things to other people, and I require the same from them. John Wayne-The Shootist