I've heard about the XM8, and that after feild testing troops reported that after so many rounds the light weight materail the XM8 was made of would start to melt. Plus it was just a modified G36, or was a very, very heavily based design off the G36. It has already been sorted out of the list of replacements for the M16, but Heckler Koch still has a few other guns they have shown to the U.S....