More Americans than ever are carrying concealed handguns, but some of these small pistols are coming under scrutiny for accidentally shooting their owners.

Travis Barthel, a 34-year-old elementary school teacher from South Dakota, was setting down his coat with his pistol made by Cobra Enterprises of Utah Inc. in a pocket. The gun fired and hit him in the stomach. The 9mm slug severed an artery, pierced his spleen, broke his ribs, and sent him to the hospital, where it took two surgeries and 11 pints of blood to save his life,...