Cheaper per round to buy it this way:
http://palmettostatearmory.com/inde...deral-5-56-55gr-fmj-bt-90rds-strclp.html12 boxes on stripper clips = $311.88 + $33.00 ship = $0.319333 per round versus $0.32599 and you get it on 108 loaded stripper clips.
Cheaper at Weidners too $349/1,200 IMI M193. IMI is good stuff.
Xm193 has always been pretty decent blasting ammo for me but never super accurate in 10 or so AR's I've owned. In my current 1-9" gun it shoots 1-1 1/2" groups routinely where as several other factory 55gr loads do much better.
Again just IMHO and my guns.
Target Sports USA usually has it for the same price shipped. The also have PMC .223 for $249 shipped once in a while.