To fire semi-auto from a closed bolt (which confers better accuracy) and to fire fully automatic from an open bolt (which cools the barrel better and prevents "cook off" -- the spontaneous ignition of a cartridge in the chamber from the heat retained by the barrel). So I see that this semi-auto version is converted to fire from a closed bolt.
This picture would indicate that it is a rotary bolt,
somewhat along the lines of an AK47.
When I say "ugly," I'm thinking of me owning a semi-auto version myself. Beauty of function is certainly there -- it's similar to admiring a moose: their adaptation for the task is quite beautiful, but the moose itself is no Venus de Milo.
On the backpack 800 round belt -- how cool! This is one thing that the opponents of 5.56x45 can't get around: being able to pack this much firepower can only be done with a small round, and regardless of the stopping power of one individual round, getting "swiss-cheesed" by the spray of this thing has got to be effective, I would think.
Being able to switch from the belt to the clips carried by M4 users is also quite an advantage.
So the Marines are switching from the M249 to the M27? I wonder how the foregoing of the belt fed feature is accounted for in their field doctrine?
