Q. OK, that's complex. Simple question: Can I fire M193 ammo in my 1:7 or 1:9 twist barrel?
M193 is essentially a "universal" round; able to be stabilized by barrels with twists between 1:14 and 1:7. Point of impact will change slightly compared to an M855 zero, so rezeroing is recommended.
Fact: The Scoop from the Army's Ammunition Information Notice (61-01) "INTERCHANGEABILITY OF 5.56MM BALL, TRACER AND BLANK AMMUNITION."
It is acceptable to use M193 and M196 ammunition in training in M16A2, M16A3 rifles and M4 and M4A1 carbines (16 percent range reduction). Substituting between types of ammunition during firing is not recommended.