Did the same swap with my 340D with a barrel from Numrich. Had to get a little creative with the barrel nut removal but after reading many threads here and other forums chose a satisfactory solution ( Kroil, an old leather belt and vice grips. No marks!!!). The other issue you will have is you need a .223 mag. They are not the same as the .222 and it will take a little finessing for a solid fit and feed. At least mine did. If it sounds like more than you planned on taking o, PM me and maybe I can help. Good luck.