Making the Case for Fast-Twist Varmint Rifles

You may be able to extend your success for long-distance predator and varmint shooting with today's superior optics, rifles, ammunition and tech support.

Making the Case for Fast-Twist Varmint Rifles

Maximizing your accuracy at long distances requires much time at the range dialing in your optics, ammunition and rifle to get the best results possible. (Photo: Roy Welch)

Long-range shooting at steel targets, varmints and big game has accelerated in recent years. This is due in large part to the availability of precision rifles, new cartridges optimized for long-range applications and superb variable-power scopes of high magnification with refined ballistic reticles. And don't forget about the inexpensive ballistic software, heavy-for-caliber bullets of high ballistic coefficient and quality custom barrels with rifling twists designed to stabilize these bullets.

Companies such as Berger, Hornady, Nosler, Sierra and Swift, responding to demand, now offer copper-jacketed, lead-core varmint bullets of increased length and weight with ballistic coefficients greater than 0.250. These bullets provide flatter trajectories, reduced wind deflection, and superior striking energies beyond 300 yards. Lead-free copper and composite bullets slightly longer than equivalent weight copper-jacketed, lead-core bullets are gaining in popularity and also require barrels of faster twist to ensure bullet stability.

Most .20- and .22-caliber bolt-action varmint rifles come from the factory with barrels of relatively slow 1:12- or 1:14-inch twists suitable for use with copper-jacketed, lead-core bullets of light to medium weight. Muzzle velocities of factory ammunition range from approximately 3,000 to more than 4,000 feet per second, and ballistic coefficients vary from about 0.170 to 0.260. These rifles, cartridges and bullets are entirely satisfactory for shots at varmints.

However, beyond 300 yards, kinetic energy falls off rapidly and the combined effects of bullet drop and wind deflection reduce hit percentages. This occurs no matter the optics or how inherently accurate the rifle-cartridge-shooter combination is at sight-in distances of 100 to 200 yards. In order to flatten trajectory, minimize wind deflection, and maximize striking energy at extended range, sleek bullets and fast-twist barrels that stabilize these bullets are required.

What is Bullet Stability?

Before proceeding, a brief explanation of what is meant by "bullet stability" is appropriate. A gyroscopically stabilized bullet leaves the muzzle with adequate velocity, spinning sufficiently fast to maintain a point-forward attitude throughout its flight. If the twist is too slow and/or the bullet design is faulty, the bullet may pitch and yaw, or even tumble, unable to regain a point forward attitude if disturbed. Such a bullet is unstable, suffering increased drag and a reduction in ballistic coefficient, which, to varying degrees, affects accuracy and the predicted trajectory, wind deflection and kinetic energy at extended range.

Bryan Litz, chief ballistician for Berger Bullets, provides a detailed explanation of bullet stability in his books, Applied Ballistics for Long-Range Shooting (2011) and Ballistic Performance of Rifle Bullets (2014).  Refined G1 and G7 ballistic coefficients and stability factors (SG) for bullets of diverse manufacture are also cataloged. A software routine based on the Miller twist rule for computing twist rates and bullet stability factors can be accessed here.

Factors of less than 1.0 define inadequate stability, 1.0 to 1.5 marginal stability and greater than 1.5 comfortable stability. Twist/bullet combinations in the marginal category may provide satisfactory accuracy and ballistic performance.

To be safe, however, a barrel twist sufficiently fast to provide comfortable bullet stability at your nominal altitude above sea level without running the risk of bullet fragmentation due to centrifugal force is recommended. The desirability of fast-twist barrels for the .204 Ruger, .223 Remington, .22-250 Remington and .22 Nosler cartridges is examined below.

.204 Ruger

Factory cartridges for the .204 Ruger feature bullets of 24 to 45 grains at muzzle velocities of 4,400 to 3,625 fps. However, factory loads with 32 and 40 grain bullets at muzzle velocities of approximately 4,200 and 3,900 fps, respectively, are most frequently encountered. Factory rifles chambered for the .204 Ruger typically have barrels with a 1:12-inch twist. Although this rate of twist has proved acceptable for 0.204-inch diameter bullets weighing 24 to 35 grains that have ballistic coefficients of 0.170 to 0.210, it provides inadequate to marginal stability for bullets of 39 and 40 grains with a ballistic coefficient of approximately 0.275 and is way too slow for the long Berger 55-grain .204 bullet that has a ballistic coefficient of 0.354.

When you're targeting coyotes or varmints, using the appropriate targets with your range practice can give you a better idea of your shooting rig's performance. (Photo: Roy Welch)

In order to realize the full potential of the .204 Ruger for both small- and medium-sized varmints at distances beyond 300 yards, bullets of 39 to 55 grains with ballistic coefficients of 0.270 and higher should be considered. A comparison of bullet height (trajectory), wind deflection and energy values for 32-, 39/40- and 55-grain bullets zeroed for 250 yards reveals only minor differences in exterior ballistics at 300 yards.

At 500 yards, the trajectory of 32- and 40-grain bullets is virtually identical, but wind deflection for the 39/40-grain bullets is reduced by about 25 percent, whereas kinetic energy is almost 60 percent greater. The 55-grain bullet has more drop than the 32-grain bullet, but both wind deflection and kinetic energy are noticeably superior. The reduction in wind deflection and greater striking energy of the 39/40- and 55-grain bullets make them effective to beyond 400 yards.

In order to achieve comfortable bullet stability, however, a barrel twist of 1:9 or 1:10 inches is recommended for the 32- to 40-grain bullets and 1:7 or 1:8 inches for the 55-grain bullet.  These twist/bullet combinations allow you to extend the distance for accurate shots on small varmints by about 50 to 100 yards. With proper shot placement, there is sufficient kinetic energy to take coyotes at distances beyond 300 yards.

.223 Remington

The majority of bolt-action rifles chambered for the .223 Remington cartridge are fitted with barrels of 1:12- or 1:9-inch twist. Savage Arms does offer Model 12 Varmint Series rifles with 1:7- and 1:9-inch twist barrels. Most AR-15 rifles, by contrast, have barrels with 1:7- to 1:9-inch twists.

The 1:12-inch twist barrels are optimal for jacketed lead-core bullets of 35 to 50 grains, but provide only marginal stability for both 55-grain jacketed lead-core and lead-free bullets. Barrel twists of 1:9 to 1:7 inches are needed to ensure adequate stability for bullets of 60 to 80 grains.

The .223 Remington loads in Table 1 for 45-, 55- and 75- grain bullets have muzzle velocities of 3,600, 3,240 and 2,790 fps and ballistic coefficients of 0.173, 0.255 and 0.395, respectively. At distances from 300 to 500 yards, compared to the 45-grain bullet with a velocity of 3,600 fps and a ballistic coefficient of only 0.173, the 55- and 75-grain bullets show flatter trajectory, reduced wind drift and approximately 170 to 360 ft.-lbs. of additional kinetic energy. It is important to note that you cannot expect the higher velocity of a lighter bullet to fully compensate for a weak ballistic coefficient.

To take full advantage of the .223 Remington cartridge, give consideration to outfitting the varmint rifle with a barrel having a twist of 1:7 to 1:9 inches and using bullets of 55 grains and heavier with ballistic coefficients greater than 0.260. The distance at which you can reliably hit small targets in light to moderate wind conditions will be extended by up to 100 yards, with sufficient energy to cleanly dispatch prairie dogs, woodchucks and coyotes. Inside 200 yards, given precise shot placement with heavier bullets designed for large varmints and game, the .223 Remington has sufficient energy for deer and small- to medium-sized feral hogs.

.22-250 Remington 

Virtually all popular brands of .22-250 rifles come with barrels having twists of 1:12 or 1:14 inches that are suitable for bullets up to approximately 55 grains in weight. The Savage Model 12 LRPV has both 1:12- and 1:9-inch twist options. The relatively slow twists and the absence of ammunition loaded with heavier bullets of high ballistic coefficient limit the long-range potential of factory 22-250s.

In order to ensure adequate stability with 55-grain and heavier bullets, a barrel twist of 1:9 or 1:8 inches is required. For example, 55-grain bullets such as the Nosler Ballistic Tip Varmint and Hornady V-Max with a ballistic coefficient of approximately 0.265, loaded to a velocity of 3,680 fps, have stability factors of about 0.8 to 1.10 when fired in 1:14- or 1:12-inch twist barrels. When fired in a 1:9-inch twist barrel the stability factor rises to approximately 2.0, which indicates that the bullet will have minimum pitch and yaw, going to sleep quickly.

A 75-grain bullet, such as the Hornady ELD-Match, Hornady A-Max (replaced by the ELD-Match), Berger VLD, or Swift Scirocco, with a ballistic coefficient greater than 0.400 and a handload muzzle velocity of 3,200 fps, has stability factors of approximately 1.2 and 1.5 when fired in a 1:9- and 1:8-inch twist barrels, respectively.

Out to 500 yards, the trajectory of these heavier bullets essentially duplicates that of the 55-grain bullet. However, the wind deflection for the 75-grain bullet ranges from about 1/2-inch per mile-per-hour of crosswind velocity at 300 yards to 2 inches per mile-per-hour of crosswind velocity at 500 yards, as compared to values of approximately 1-inch and 3-inches per mile-per-hour of crosswind velocity for the 55-grain bullet.

The kinetic energy of the 75-grain bullet at 300 yards is about 40 percent greater than the energy of the 55-grain bullet, increasing to approximately 80 percent greater at 500 yards, making the 75-grain bullet suitable — with proper shot placement — for shots at coyotes out to plus 500 yards, and deer and hogs to approximately 200 to 250 yards (Figure 3).

An indication of the additional yardage gained with the 75-grain bullet, as compared to the 55-grain bullet, is obtained by noting that a 10 mile-per-hour crosswind deflection of about 17 inches for the 75-grain bullet at 500 yards is roughly equivalent to that of the 55-grain bullet at 400 yards, and that the kinetic energy of plus 800 ft.-lbs. at 500 yards closely approximates that of the 55-grain bullet at 300 yards.

Based on exterior ballistics, the 75-grain bullet adds 100 to 200 yards of effective performance.  Extensive field experience gained from shooting prairie dogs with fast-twist .22-250s at distances greater than 300 yards confirms that the range for acceptable hit percentages is extended by about 100 yards when using the 75-grain bullets in rifles with 1:8- and 1:9-inch twist barrels.

.22 Nosler

The popularity of the AR platform and the desire for an AR compatible high-velocity round that approaches the performance of the .22-250 Remington cartridge led Nosler to develop the .22 Nosler cartridge, released in 2017. This cartridge closely resembles a necked-down 6.8 Remington SPC cartridge, but has a rebated case rim that matches the 0.378-inch diameter of the .223 Remington/5.56 NATO case. Case capacity falls midway between that of the .223 Remington and the .22-250 Remington. An overall cartridge length of 2.260 inches enables the use of standard 6.8 SPC AR-15 magazines. All that is required to convert a .223 Remington/5.56 NATO AR to a .22 Nosler AR is a new barrel (or upper) chambered for the .22 Nosler cartridge and a supply of 6.8 SPC magazines.

Recognizing the increased interest in long-range shooting and the need to accommodate heavier bullets, Nosler wisely chose 1:8 inches as the appropriate twist for .22 Nosler barrels. A 1:8-inch twist fully stabilizes bullets of 55 to 80 grains, ensuring that ballistic software predictions of trajectory and wind deflection will prove reliable. Nosler factory ammunition with 55-, 62-, 70- and 77-grain bullets is now available.

Exterior ballistics for factory rounds fired in an 18-inch barrel specify a muzzle velocity of 3,350 fps for 55-grain Nosler Ballistic Tip Varmint bullets (B.C.= 0.267) and 2,950 fps for 77-grain Nosler Custom Competition bullets (B.C.= 0.340). Muzzle velocities of 3,500 and 3,150 fps are listed for these loads in a 24-inch barrel. Beyond 300 yards, the 77-grain factory ammunition offers a slight advantage in wind deflection and provides an additional 170 ft.-lbs. of kinetic energy.

In the field, using an ODIN Works upper with a 18-inch barrel of 1:8-inch twist mounted on a Stag AR-15 Varminter lower, the Nosler 55-grain load was preferred for shots at prairie dogs out to 400 yards (Figure 4). To fully realize an extended range potential for the .22 Nosler that is comparable to the .22-250 Remington, a 22- to 26-inch barrel with a 1:8-inch twist is required.

Based on comparative ballistics and field experience, fast-twist barrels on varmint rifles allow the use of conventional and heavy-for-caliber bullets that are fully stabilized, ensuring flatter trajectory, reduced wind deflection and superior kinetic energy beyond 300 yards. Depending on environmental conditions and cartridge, bullet and load selection, the range at which a high percentage of accurate shots can be delivered is extended by approximately 50 to 200 yards.


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