[Myrddin]

The initial run of M16 rifles for Vietnam had rifling at 1:14 or 1:12. Not fast enough to stabilize a 55 gr .223 bullet. Poor long range accuracy and a horrific tumbling terminal performance. Current rifles are 1:8 or 1:7 to stabilize 62 gr to 69 gr bullets. It was just a poor spec at the start. A .22LR 40 gr bullet is fine with 1:12 or 1:14 rifling twist. A 1:9 is satisfactory for 55 gr bullets.

[Bikkuri]

Don’t forget the sand/mud jams of the original M16 :/