I recently purchased 2 (unissued) Yugo SKS's 1 to keep stock and 1 to modify. While searching for a muzzle brake, I came across several websites that talk about the legality of modding the SKS. Since it would seem from what I have read, that changing a C&R firearm in pretty much anyway negates its status as a C&R firearm, I am now wondering what I can "legally" do to guns I bought with my CR license???? The SKS's are an extreme case for modification, in that you have 922r to deal with once you change the firearm and its not CR compliant anymore, but what about a mauser or mosin? If I wanted to put a new bolt, stock, even barrel on my 98 or 91/30 can I legally do that to rifles I purchased with my C&R? Will ATF have a fit if they inspect me and my 91/30 is in a synth stock, with a cut down barrel, and scope mounted? I realize that once I modify a firearm and it isn't CR compliant anymore I couldn't transfer it as a CR weapon, but how does modding it affect my inventory in the eyes of the ATF?