A bullet is stabilized by spin. If the barrel spins it too slowly, a long, heavy bullet tumbles. The match between twist rate, bullet length and weight decides accuracy more than most buyers realize.

What twist means

A twist of 1:7 means the rifling makes one full turn in seven inches. A faster twist, with a smaller second number, stabilizes longer and heavier bullets. Too fast a twist is rarely a problem for ordinary bullets, while too slow a twist is a real one.

The .22s

AR-15 barrels in .223 are commonly 1:7, 1:8 or 1:9. A 1:7 or 1:8 barrel handles bullets up to about 77 grains, a 1:9 up to about 69, and older 1:12 barrels favor bullets of 55 grains or less. Norma's .223 loads are at norma 223 ammo.

The 224 Valkyrie was designed around long, heavy bullets and a fast twist, and its barrels typically use a 1:7 twist. Its loads are at 224 valkyrie ammunition.

The .24, .27 and .28

Most .243 Winchester rifles use a twist between 1:9 and 1:10, which suits bullets of about 100 grains and under, and 100-grain loads are at 243 100 grain ammo.

The .270 Winchester usually has a 1:10 twist, and polymer-tip loads for it are at 270 polymer tip ammo. The .280 Remington's twist differs among makers, so check the barrel or the maker's specification before choosing a heavy bullet. Remington's .280 loads are at remington 280 ammo.

The .30s

The 300 Blackout uses a fast twist, typically 1:7 or 1:8, so that its heavy subsonic bullets stabilize. Its loads are at 300 blackout ammo for sale.

The .308 Winchester is typically 1:10 in modern rifles, with 1:12 in some older ones. Anyone who wants to buy 308 ammo should still check the twist if they plan to shoot heavy match bullets.

The .300 magnums are often 1:10 as well. The 300 Winchester Magnum's loads are at 300 win mag ammo. The 300 WSM's 150-grain loads are at 300 wsm 150 grain ammo.

Surplus Lee-Enfield rifles use Enfield rifling, with five grooves and a left-hand twist, and their bores can vary with wear. Have a gunsmith check the rifle before shooting plain FMJ loads such as those at 303 british fmj ammo.

Barrel length

Shorter barrels lose velocity. The 300 Blackout was designed to work well in short barrels, while magnums such as the 300 Winchester Magnum work best with 24 inches or more.

Twist rates differ by rifle and maker. Check your barrel's twist before choosing a heavy bullet, and confirm current stock and state shipping restrictions before ordering.