The M-16s we had at Knox were a mish-mash, some of them still had A1 handguards that rattled around, there was daylight between the uppers and lowers, there was so much play in the fit I was nervous to fire them. Since it was at the Armor Training Center, and they don't emphasize rifle training as much, (or at least they didn't when I was there, precisely 15 years ago,) these rifles were stripped more than they were fired. If you were tricky, the handguards were a one-hand job. I had a rude awakening, when I got out and a friend of mine bought a new Colt Hbar. I thought the ring and spring were defective, they were so stiff. He had to tell me this is how they normally are.