Interesting...

[Baeron Gredlocke]

Go take a look at the bottom of this page:
http://www.4plc.com/prototype.html

And then go check out the illustrations of ACR's in your Central Supply Catalog.

 

[barnest2]

It's an XM8, an experimental modular rifle which the US military was going to incorporate, up until the point where they decided that just upgrading the M4 was a better idea.
here, a free link for you sir http://en.wikipedia.org/wiki/XM8

 

[Baeron Gredlocke]

Ah. Cool!