Smith and Wesson has a new AR platform rifle out for their M&P-15 line of rifles. What sets it apart from the current platform is that it's chambered for 5.45x39, the Russian service rifle cartridge. The advantage here is that mil-surp Russkie 5.45 is cheap and plentiful, and according to S&W will feed reliably in the new MP-15R.
The rifle has all the standard doo-dads you'd expect to see in a modern AR, a six-position collapsible stock, flattop receiver, 30 round magazines, chrome lined barrel, etc.
Obviously, the biggest benefit to this new rifle are the huge and widely available supplies of surplus 5.45 Russian ammo; you can buy spam cans full and full of ammo for half the price of 5.56 ammo; and since the Russian round delivers similar ballistic performance you're getting pretty decent bang for your buck in terms of a defensive rifle.
One thing that S&W does caution about are the magazines. While the 5.45 and 5.56 cartridges are dimensionally similar enough that you can feed 5.45 in a standard 5.56 AR magazine, the feed lips and followers are different enough that it is likely that you'll encounter feed jams trying to run the 5.45 through a 5.56 magazine. S&W recommends that you stick with their 5.45 magazines for the M&P-15R.
With the economy being what it is, and ammo prices through the roof, the ability to shoot the cheap and readily available mil-surp ammo really makes the M&P-15R appealing for me. Since I'm starting the process of AR shopping, I'm going to seriously consider an AR in 5.45 Russian. It gets cool points for being an evil capitalist rifle chambered for the former Soviet Bloc service cartridge.
