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ARMAG

Search matches names, aliases and the text of every page. An arm found by its service designation is found by its alias, not its title.

Rifling twist

The distance in which the rifling makes one complete turn, and so how fast it spins a bullet.

Also called Twist rate

Recorded here in millimetres per turn, because that is how European standards and most military documents state it: a twist of 178 mm means one full rotation in 178 mm of barrel. English-language sources usually write the same thing as a ratio, 1 in 7 inches.

The rate has to match the bullet. A longer, heavier projectile needs a faster twist to stay point-forward; too slow and it tumbles, too fast and a thin-jacketed bullet can come apart in flight. The M16’s change from a 1-in-12-inch twist to 1-in-7 between the A1 and the A2 was made to stabilise the longer SS109 bullet, and it is why the two rifles prefer different ammunition.