This topic was actually posted a while back. The SR47 prototype was a dedicated Russian 7.62 cal shooter that used AK mags; operating design appeared to be standard AR. It had a flat top & RAS fore-end rail, KAC flip-up sights, etc. A lot of buzz surrounded it. Supposedly, specops/specwar wanted something w/ more punch at longer ranges, & Knight's produced the SR47 as a potential solution.
I'd like to see the PM article myself, because it must have been wrong about the "dual caliber" capability. How can an autoloader fire both 5.56 & 7.62 from the same upper, using the same bbl? Seems a physical impossibility.
The recent skuttlebut I've heard is that a new 6.8 mm, rebated rim cartridge is being considered for the current AR platform, since it allows the current upper to be used, requiring only a new bbl. (& possibly a few other internals) + mags.