Just came upon your thread after reading up on the Cobb MCRs. It seems like an excellent idea for a rifle system, but I'm not seeing them for sale except one to bid on.
So, like any AR type rifle, you know how you can replace the upper receiver in different calibers that are of the appropriate length to fit the magazine well? Well with the Cobb MCR, the magazine well section is also modular, so you can pop off the .223/7.62x39/6.5 Grendel length magazine section(MCR-100 series) and go to the 308/243/358 lengths (MCR-200). That by itself is pretty awesome to me, but wait, there is also the MCR-300, 30-06 length rounds, and then even the MCR-400, which is for 338 Lapua, 375 H&H, 458 Winchester and many others in that magnum length group. They also make a .50 BMG bolt action set up, but I haven't looked into it yet if that upper also goes on the lower that is in the MCR series, or if there is a modular magazine section for that. Anyway, sounds like it's opening up a very expensive can of worms for someone like me who would like to have a modular kit with at least three caliber options. I can see it for some kind of Red Dawn scenario, carrying it around in a 16" M-4 configuration in general, probably in 5.56 for ammo availability, and having a couple barreled uppers on my back quick and ready to access, one in 30-06 perhaps, and then a 338 for whatever the situation may call for. Of course I'd still have a sidearm to go with that, probably a Glock 21.
