Does anyone know about the .308 M-4 type rifle? More specifically is the .308 conversion that you can get for the Bushmaster XM-15 worth getting. Is it a smooth transition or are there side effects? Does the weapon still maintain its functionality or is it prone to manfuntion? I also hear there are companies that manufacture the .308 M-4 style so a conversion is not needed. any insight on this would be appreciated.