How Twist Rates Affect Bullet Performance

Bullets fly straight when spun by a barrel’s rifling to spiral downrange like a well-thrown football.

How Twist Rates Affect Bullet Performance

Check barrel twist rates if you favor long bullets with high ballistic coefficients. They need fast spin.

Even gentle twist rates in hunting rifles induce dizzying spins. A bullet rotating one turn every 12 inches at a velocity of 3,000 fps rotates 1,500 times in half a second and 400 yards of travel! In contrast, a V-6 engine pulling a pickup at 65 mph turns about 3,000 rpm. That’s 50 crankshaft rotations per second or just 25 per half-second.

Until recently, standard rifling twist rates worked for any hunting bullet because the heaviest were all blunt, thus no longer than lighter pointed bullets. Fast-twist barrels appeared for the .223 Rem. when shooters began using it at distance with long, sharp 60-, 70- then 80-grain match bullets. Standard 1-in-14 pitch gave way to rates as sharp as 1-in-7.5. Woodpecker-nosed 6.5mm-, 7mm- and .30-caliber bullets now crowd the starting line in races to claim the highest ballistic coefficient. The longest beg extra-fast spin. Bullet-makers and loading manuals have begun to note bullets that call faster-than-factory rifling twist. If you plan to use long bullets, check the specified twist of that new rifle before you buy it, lest you find those bullets spraying pie-plate groups — or perforating 100-yard targets sideways.

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