|Originally Posted By Lester_Burnham:|
|Originally Posted By 1911greg:|
|Originally Posted By FLAJD11:|
I think the twist of the barrel rifing on the M16A2's and later variants does not work as well with M193. Civvie rifles usually have an in-between twist. If there are old M16A1's there, there is probably M193.
Your link say NOPE:
|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.
Q. Will M193 be accurate in a 1:7 or 1:9 twist barrel?
It may be marginally less accurate due to the fast twist rate, particularly in 1:7 twist barrels. Unless you're trying to use these rounds for benchrest shooting, though, it shouldn't be enough to matter.
A bullet's flight is disrupted slightly as it leaves the barrel and after traveling some distance, will "settle down" into an even spiral, similar to a thrown football. The faster a bullet is spinning, the longer it takes to settle down. The most accurate twist rate for any length of bullet will be just a bit faster than what is required to stabilize it for its entire flight path (1.3 SG). But note that bullet quality plays a much bigger part in this equation. A uniform bullet will spin true; a non-uniform bullet will wobble and be inaccurate. As a general matter when shooting M193 or M855 (as opposed to match ammo) its better to err on the side of a faster twist rate. Regardless, both 1:9 and 1:7 twists seem to shoot M193 and M855 very well.
M193 is not issued because it is no longer made. It has nothing to do with not working in faster twist barrels.
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