Yes, I do have proof.  Rock River Arms has a patent application filed for a 308 rifle.  It's detailed and looks EXACTLY like the Bushmaster BAR-10.  I wonder if Bushmaster had a license to produce the weapon or if there was some sort of corporate deal that I was unaware of.  If you can look up a patent, here's the application link:

appft1.uspto.gov/netahtml/PTO/srchnum.html

It's application # 20050183310 for the record.  You'll need AlternaTIFF viewer which is a plug-in you can get here: www.alternatiff.com/  If you just click on the button to auto-install it, that should work.  It's selection 1.

It was rumored that Rock River sold the design to Bushmaster. It was also rumored that they sold it due to extreme problems with the bolt assembly and the FAL mags clashing.

I believed this rumor, as it became obvious awhile after, that there actually was a problem with getting the FAL mags to work with out causing heavy stress on the bolt assembly (In the Bushmaster BAR10). This rumor is even more believeable as Rock River did have such a design patented.  

ETA: I wish I could down load the stuff needed to view the picture.

Hadn't heard the rumors myself, but sure looks plausible now.  Random patent application searches work well, don't they?  So the bottom line is that Bushmaster bought an interesting design that was difficult to get working correctly?  When I handled the BAR-10 at the SHOT Show, I was thoroughly unimpressed.  It looked good, but the magazine release and bolt catch were difficult to operate.  Never had a problem with my AR-10B or the DPMS .308.  

Santa tag

Someone posted on here way back when that they had toured one of the subcontractors (Continental Machine, maybe?) and had seen some .308 receivers being machined for RRA.

The thread died a pretty quick death, because nobody believed the guy.