As far as I know, the twist rate for the M193 load was 1-12, but that was for the M16A1 rifle. Apparently, it was 1-14 for early M16 series rifles but they went to the 1-12 later on. The M16A2 variant used a fast 1-7 twist because of the length of the bullet used in the M856 tracer loading. I'm pretty sure the M16A4 used the 1-7 twist also as do the M4 series rifles. When I was in the military, we were taught that the M193 could be used in the 1-7 twist M16A2 rifle, but that the maximum effective range would be reduced because of the lighter bullet.
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