In which wars would I have been able to turn the tide with an M-16?

I'm not sure. Snipers and bowmen have been around for centuries. And other guns have been around a long time, too. If you went back, against muskets, you could win a few battles, but you would be effected and probably killed more by numbers then their weapons. Good luck, go for Switzerland, they would probably surrender are fear you like a god.