Best bullet for an ar15

Answer 1

That depends on what its chambered for....

Most AR-15's are chambered for the standard 5.56x45mm military round, although some will only have a .223 Remington chamber, and it not advisable to fire 5.56 rounds through these. There is also the .223 Wylde, which can handle all loadings of 5.56 and .223.

Most commercial AR15 rifles will come with a 1:9 barrel twist rate, which can accommodate both the lightweight 45 and 55 grain commercial .223 and M193 cartridges, as well as the heavier 62 grain NATO cartridges. However, when you get into loads such as the 77 grain rounds, the 1:9 barrels won't stabilise them very well. 1:8 barrel twist is the most dynamic, and can handle anything from 55 grain .223 and M193 up to the 80 grain .223 Wylde, and everything in between. 1:7 twist is a bit too fast a rifling twist for the lightweight 45/55 grain .223 rounds and the 55 grain M193 rounds, and really is a bit excessive a twist rate for the 62 grain M855/SS109 (NATO standard) cartridges. But it's great for 75, 77, 80 grain projectiles.