Why 1/12 twist?

[SoDak]

I bought an M16A1 upper recently and I got to wondering about why did these guns use a 1/12 twist? Was it just that no one ever figured on using a heavier bullet weight so this worked fine or are there other reasons?

[ABNAK]

@SoDak

I bought an M16A1 upper recently and I got to wondering about why did these guns use a 1/12 twist? Was it just that no one ever figured on using a heavier bullet weight so this worked fine or are there other reasons?

Pretty much.

It was actually 1:14 (!) before mods were made—IIRC that was one of the initial mods made. It didn’t shoot accurately enough under Arctic conditons with a 1:14 twist.