My two best shots both involve M-16A2's.
The first one was during Basic Training, at Ft. Benning, GA, fall of '89. We were doing our Basic Rifle Marksmanship qualification. I had had to pull SPORTS early during the itiration, so when I shot the 39th target, my bolt locked to the rear, as I had ejected a round while fixing my malfunction. Without thinking about it, I looked over, grabbed the round, threw it into the ejection port, hit the bolt release, and hit the 40th target. I ended up with a Sharpshooter qualification, and the Drill Sergeant's praise, as he was standing over my shoulder when I did it. Made me feel like John Wayne or something.
The second one was at Grafenwohr, Germany, summer of '91. We were doing Squad Live-Fire Lanes, at night, using a trench line to engage targets ranging in distance from 100 meters to 800 meters. The SAW gunners were supposed to engage the 800 meter targets. However, one SAW didn't have a night-vision scope, and the other's wasn't zeroed. In fact, I had the only weapon with a zeroed AN/PVS-2 in the squad. After the SAW gunners missed all 8 of the first set of 800 meter targets, I decided to engage the next batch. I hit 6 of the 8 before the other two went back down. I also hit 6 of the third string of 8. Granted, it took me about a full mag to hit those 12 targets, but, how many people can say that they've SUCCESSFULLY engaged man-sized targets at night, with an M-16A2, at a range of half a mile?