The New York City Police Department, for example, has long encouraged backup guns, but they allow only two calibers: 38 Special in a revolver, and 9mm Parabellum in a semiautomatic. This is the result of long institutional experience encompassing a great many gunfights, and it embodies common sense.
As this is written, there are at least five state police agencies that issue backup handguns to all their troopers. Two of them consider commonality important issuing Glock pistols in two sizes and the same caliber. One agency issues the standard size Glock 37 and “baby” size Glock 39, both in 45 GAP. The other issues the 5.3-inch barrel Glock 35 and the 3.6-inch barrel Glock 27, both in 40 S&W. If the primary weapon is lost, snatched away, or damaged, the trooper still has a spare pistol and two spare magazines to fight with, because the smaller Glock will take the larger Glock’s magazines in the same caliber. Similarly, the G26 subcompact will accept the magazines of the compact G19 or full size G17 in caliber 9×19, and the subcompact 357-caliber G33 will work with the same-caliber magazines of the compact G32 or the full size G31.
The other two state police agencies in question take a different route. One has issued the Beretta 380 for the backup role, while equipping its uniformed personnel with full size Beretta 9mm and 40 pistols over the years. With a recent switch to the Glock for duty, that department may soon be trading its 380s for baby Glocks in a more potent caliber. Another agency has issued snub-nose S&W revolvers for decades as backup, the current gun being the Model 640-1 in 357 and loaded with 38 Special +P+, complementing a SIG P226 duty weapon in 40 S&W. Within the last couple of years, a fifth state police department has bought S&W 38 Special Airweights for all troopers, in addition to their standard issue 357 SIG pistols.
Each person in the private sector must make his or her own decision. Certainly, the ability to interchange spare ammunition between the backup gun and the primary is a real “plus.” For many decades, cops carried their spare 38 Special ammo loose in pouches or loops, and were encouraged to get a smaller 38 Special for backup for just this reason. Indeed, they were taught that if they carried a Colt as primary they should carry a Colt as backup, and ditto with Smith & Wesson, because the cylinders would rotate in the same direction and open the same way.
In the 1970s, revolvers still held sway in police work, but speed loaders became accepted duty gear. It was discovered that the speed loader sized to fit a K-frame Smith & Wesson service revolver would fit perfectly in a six-shot D-frame Colt backup gun. The hot set-up became a four-inch or six-inch Smith 38 or 357 in the uniform holster, and a two-inch Colt as backup gun, with the speed loaders filled with hot 38 Special ammo that could be fired from either revolver.
Today, with autoloaders so hugely popular, commonality is still a factor, but not always. Certainly, Glock interchangeability makes huge sense. Someone carrying a double-stack S&W 9mm of conventional size can carry a Kel-Tec P11 for backup, secure in the knowledge that the 14.5 ounce 9mm Kel-Tec will accept the magazines of a Smith & Wesson 5906 or 6906 in the same caliber. If the full-size or Commander-size 1911 is chosen for primary, a subcompact such as the Colt Defender can work with full-length magazines in the same caliber in an emergency, but those longer mags can over-travel and lock up the gun when slammed into a full-size 1911 that’s at slide-lock.
Many backup gun users have decided to do without ammo interchangeability in the name of convenience, concealment, or faster tactical access. Some just don’t happen to have a primary gun that’s magazine-compatible with a smaller one for interchangeability. For instance, this writer’s department issues the Ruger P345 as a duty pistol, and this 45 auto does not have a subcompact version available. Accordingly, each officer is issued a Ruger SP101 357 Magnum snub-nose revolver for backup, and most carry a Bianchi Speed Strip with spare 357 rounds somewhere on their person while at work.
“Civilians” and police officers alike have found that while autos might be a better choice as primary weapons, revolvers may be preferable as backup because of faster access out of pockets due to their rounded grip-frames, or better resistance to dust and grit when carried in ankle holsters. Another advantage of the small revolver for backup comes in one of the applications mentioned earlier in this article, the use of the backup to arm another competent good guy or gal. You may not have time to explain to that person how your auto works or why they need to keep their weak side thumb out from behind the slide when you hand them your backup auto. However, anyone competent to wield a gun in a crisis situation will be competent to handle a double action only revolver when there is no time to explain the “manual of arms.”