@ Dimitriy, you should invest in an AR-15. It's the civilian availible version of those two guns. If you have the aptitude you could also just build one from a kit. (all my posts seem to come back to the AR. Lol)
@Meat, yeah, the H-bar is a pretty popular addition, it keeps the barrel cooler due to it's mass, and let's the gun stay accurate over long firing times.
@Digital Vulp., I aphadnt thought about the licensing thing, but there are so many people who make so many versions of the same gun, what does it matter? I dunno about the first part, it didn't stop CoD at all..