Right, it's just an AR-15 (the civilian version of the M-16). There are several manufacturers of this gun. Bushmaster is just one of them. Your pic is of a Bushmaster with some added bells and whistles: scope, tripod, and perhaps a bull-barrel (a heavier barrel for long range shooting). If you just walked into a gun shop and said you wanted a Bushmaster AR-15, you'd probably be handed something that looked a little more like this (i.e., without all the bells and whistles):
If you just walked into a gun shop and said you wanted a Bushmaster AR-15, you'd probably be handed something that looked a little more like this (i.e., without all the bells and whistles):To be more accurate, you wouldn't be handed the rifle, you'd have to go through a background check and fill out a government form first.
All that before handing over the ca. $1000... (soon to be more, much more...)