Rifle: AR-15 or anything chambered in .223 Remington since it has nearly the same external dimensions, military cases are thicker for greater powder capacity then commercial cartridges. I personally like the ANSCHÜTZ Model 1770 and Ruger Mini-14 for this calibre. As for pistols you will probably being using Beretta 92FS in most branches of the US Military. So go with 9mm for now.
http://jga.anschuetz-sport.com/index...uktShow=detail http://www.ruger.com/products/mini14/index.html