With a 5+1 capacity, the Back Up was just 5-inches overall due to its abbreviated 2.5-inch barrel. Height, the main concern for a pocket pistol, was just 3.5-inches. The weight of the all-metal gun, whose only non-steel components were the later adoption of carbon fiber grips, was a hefty 18-ounces, which is notably about twice as much as today's Ruger LCP, a handgun with the same rough dimensions, caliber, and capacity.
At the time the Back Up debuted, most pocketable semi-autos were small .25ACP models such as the Browning Baby or Colt Junior. Compared to these legacy guns, which were either blued or nickel-plated steel and prone to hard wear due to their philosophy of use, the stainless Back Up in a larger caliber was an easy choice, especially for deep and ankle carry.
The guns found a niche market as, when they were introduced, they were billed correctly as the smallest .380 available. Advertising from the era described the gun as "reliable pocket protection for civilians and security personnel." The design incorporated both a frame-mounted manual safety and a beavertail grip safety to provide peace of mind for those who carried the gun fully loaded.
The Back Up series was far from perfect. Sights were crude, triggers were creepy and inconsistent, and they used a funky heel-release magazine format. Worse, barring proper throating of the barrel, they rarely ran well with hollow points, although all these factors were improved on later examples after a post-1992 redesign.
Still, they remained in production with AMT off and on for decades with the successive Irwindale Arms Incorporated, Galena Industries, and High Standard companies keeping the Back Up in catalogs into 2018 when the latter closed shop. The gun even popped up in Breaking Bad in the hands of cooking enthusiast Jesse Pinkman.