Ok here are a bunch of pics of my Mil Spec AR-15. There are a few noteable differences. The first is the snake emblem on the mag well is not present on military rifles, that is the logo for Bushmaster, the manufacturer of my particular rifle. Military rifles were made by Colt, Singer, S&W, etc. The design is Colt, but licensed to others to be able to meet with demand. Speaking of which if you ever run accross one made by Singer, and have the $$, buy it. It's EXTREMELY valuable. Anyway.... Also on the fire/safe switch, the military has a third position. The three positions are labeled safe, single, burst/full. Granted on that tiny scale you wouldn't be able to read it, but a squiggly line at all three positions to indicate something is there might be in order. The other main differences would be the handguard on SOME rifles will be different. Same with the flash supressor. Actually on mine it's not a flash supressor it's a compensator. The flash supressor would have the holes going all the way around. Notice the flat spots at the rear of the flash supressor, that is for the wrench to remove it and replace it or to attach a sound supressor in it's place(rare). Most American GI Rifles, I've noticed have the solid non adjustable stock, as well as the slab sided handuard on the front end. Also take note of the little release lever on the charging handle.
Also at the very bottom is an open close picture of a military surplus M1919 .30 Cal Browning. The internal part of the sideplate has been machined to make it semi-auto, it belongs to a friend of mine. The ammo can is correct, and the can holder was made using blueprints for the original military piece. Same with the pintle if you can see it. The difference is, on the military version, the ammo can holder is mounted to the pintle and doesn't move with the gun like the one in the picture does.
I can also do pictures of a WWII Russian Battle Rifle, including the bayonet, sling, cleaning kit, and the oil can. Mine was manufactured in Russia in 1939 if I remember correctly, I would have to double check my research sheet.