Shotgun Derringer is the best 2 shot backup

The Bond Arms Texas Defender is a compact heavy hitter that makes a great backup.

It’s only got two shots, but those shots are both .410 shells. With interchangeable barrels, this Derringer can fire a wide range of ammunition including .22 lr, 10mm Magnum, .357 Magnum, .40 S&W, .45ACP, and .45 long colt or .410 shotgun shells.

Based on the Remington Model 95, this is basically a century old design on steroids.