There’s a good reason to carry spare ammunition – magazines fail, you might need more than X number of shots – or possibly a backup gun. A great of police officers carry one, as do a great number of concealed carriers whether it’s a snubby or micro .380 in a pocket or an ancillary pistol in a concealed carry holster away from the dominant carry position.
After all, many a peace officer in the days when revolvers were the issue gun of the day carried their 4-inch Model 10, Colt New Service or Police Positive, Ruger Security Six and so on with a 2-inch snub in the pocket as a backup gun. While many officers would carry speedloaders as a matter of course, resorting to the BUG – as it’s often called – was said to be more common than reloading for many.
In fact, multiple wheelguns was a practice for almost as long as revolvers have been around. Carrying multiple pistols was a standard practice in many cavalry units. Members of Mosby’s Rangers, a Confederate cavalry unit, were known to carry four: two in belt holsters and two more on the saddle or in their riding boots.
Some have taken to calling it carrying spare ammunition with another pistol wrapped around it, which in this era of autoloaders is especially handy when carrying pistols that accept the same magazines such as Glocks, Smith and Wesson M&P double-stack models, etc.
However, packing not only spare ammunition but a spare gun to go with it is cumbersome. That’s a lot of hardware to carry on a regular basis. A magazine or two is a lot more manageable.
http://dailycaller.com/2017/07/08/ccw-weekend-carry-a-back-up-gun-spare-ammo-or-both/