Date: Jan 01 2007
Many shooters and even some supposed professionals are confused by rifling twist. First, there’s the assumption that bullet weight is the primary factor in how “fast” a twist is necessary to stabilize a bullet. Nope. The correct twist involves the length of the bullet, which can be affected by ogive or base shape (roundnosed or spitzer, flat-based or boat-tailed), material used (lead, lead-core or some lighter metal such as copper) or plastic tips. A roundnosed 220-grain .30-caliber bullet, for instance, is these days often no longer than a boat-tailed, plastictipped spitzer – and both require the same twist for stabilization.
There’s also still a hard-lingering assumption that a bullet should only be stabilized as much as it needs to be. Using a faster twist, we hear, will “over-stabilize” the bullet and wreck accuracy. This is also wrong, at least with well-balanced bullets – and the majority of bullets we have today are very well balanced. The most extreme example I’ve dealt with was a custom .260 Remington I once owned with a 1-in-8-inch twist. In theory this was just right for stabilizing the longest 6.5mm bullets, such as the 140-grain Barnes X and 156-grain semi-spitzer Norma Oryx, but would be far too fast to work with varmint-weight bullets such as the 85-grain Sierra HPBT and the 95- grain Hornady V-MAX. Wrong again. It shot ALL those bullets into five-shot groups under an inch at 100 yards.
Also, rifling twist can affect stabilization of the bullet after it hits game. This is most common with “solids,” bullets designed to retain their shape rather than expand, whether cast of hard lead alloys, jacketed or made of solid copper or bronze. Some hunters of large, dangerous game prefer faster twists than when using solids made from copper alloys. These are longer than traditional lead-based solids, so can veer off course when they hit game if not somewhat “over-stabilized.” The denser air at lower elevations also requires more twist for bullet stabilization. This is why a rifle that will be shot at widely different elevations should have a twist that will stabilize its longest bullet at any elevation. All of the above reasons are why I tend to select a faster twist than standard for many cartridges, from .22 centerfires on up. A 1-in-9-inch twist .223 Remington, for instance, will shoot very well with traditional varmint bullets up to 55 grains, but will also handle longer bullets of 60+ grains for very long-range shooting.