.38 Long Colt - Design and Ballistics

Design and Ballistics

The 38 Long Colt's predecessor, the 38 Short Colt, used a heeled bullet of 130 grains (8.4 g) at a nominal 770 ft/s (235 m/s) producing 165 ft·lbf (232 J) of muzzle energy. The cylindrical "shank" or "bearing surface" of the bullet, just in front of the cartridge case mouth, is .374 or .375 inches (9.50 or 9.52 mm) in diameter, the same as the cartridge case (exactly like the .22 rimfire cartridges). A smaller-diameter portion of the bullet, the "heel," is crimped inside the case mouth, and the lubricant is outside the case, and exposed.

In contrast, the 38 Long Colt uses a .357–.358-inch (9.07–9.09 mm) bullet, the bearing surface and lubricant of which are entirely contained within the cartridge case. This keeps the waxy lubricant from collecting grit which can damage the revolver's barrel. Unfortunately Colt retained the single-diameter charge hole, so the bullet was grossly undersize as it traveled through the chamber throat. It was supposed to expand in the throat and be "swaged down," or reduced again in diameter, as it entered the barrel, but expanded unevenly producing poor accuracy. Velocity was the same 770 ft/s (235 m/s), but bullets weighed 150 grains (9.7 g), resulting in a muzzle energy of 198 ft·lbf (268 J).