Being the sooper espert you are, you don't know the difference in the external difference between a Colt AR-15 Model 601 (M-16) and a Colt M-16 Model 602 thru 602. You won't answer that question because you don't know. Well, cupie, I have fired ALL the variants. And you uber gunnutters are so misinformed that your opinions don't count for anything in any conversation. In fact, you hurt any legislation for or against gun regs.
Here is the answer to that question. It's the charging handle. The original AR-15 Model 601 was NOT called a M-16 because it predates the M-16. But it begat both the AR-15 and the M-16 Model 602. The M-16 uses a T handle while the Model 601 uses or used a diamond charging handle. But as the charging handles on the 601 was replaced, it was replaced by the T handle. ALL parts are interchangeable and have been since 1959. The Army got their hands on a few Colt AR-15 601s and tested them and found them to be an adequate replacement for the M-14 and the M-1A1. The Marines and Navy follow suit. Colt then made the Model 602 which had the M-203 rails that were added to the 601s as a Mod. When that mod was done on the 601, it was restamped AR-15 Model 601 (M-16) while the 602 was stamped M-16.
If you handled a M-16 prior to 1992, you may have held an AR-15 Model 601 (M-16) and not even been aware of it. Of course, you are too stupid to know the difference anyway.