Colt .36 Caliber to .38 Caliber Conversions

The .36 caliber percussion revolver barrel has a bore diameter that is supposed to be .375 inches. More important is the fact that today’s .38 caliber cartridges are loaded with .357-inch diameter bullets. That's about an .017 to .018 differentce in bullet size to barrel size. And on the replicas, not all the barrels measure out to exactly .375 inches. As you can see in Fig. 1, my '51 Pietta Colt Navy measures at the crown about .355 1/2 and at the forcing cone .375. The Howell cylinder I have has chambers of .374.

Due to these measuremnts of the .375 barrel and the .357 bullet diameter, in order to attain accuracy with a modern .38 Long Colt caliber cartridge in the reproduction .36 caliber percussion revolver conversion, you must shoot soft lead .38 Special, hollow base wad cutters, .38 Long Colt hollow base or .38 Long Colt healed ammunition so as to compensate for the .375 measurement. The soft lead hollow base bullet will “bump up” to the .375-inch bore diameter through obturation, the result of a bullet or pellet expanding or upsetting to fit the bore, and shoot more accurately. A bullet made of soft material and with a concave base, will flare under the heat and pressure of firing, filling the bore and engaging the barrel's rifling. The mechanism by which an undersized soft-metal projectile enlarges to fill the barrel is, for hollow-base bullets, expansion from gas pressure within the base cavity and, for solid-base bullets, "upsetting"— the combined shortening and thickening that occurs when a malleable metal object is struck forcibly at one end.

The chambers of the conversion cylinders will accept .38 Special hollow base wad cutter cartridges but the cylinder is too short for and is not intended for use of the .38 Special standard cartridge. They must be hollow base wad cutter bullets or heel base bullets . The cylinder has been made this way so that the shooter can use commercially loaded hollow base, soft lead bullet ammunition. It is very important to remember that the cylinder it is not intended for the standard .38 Special cartridge.  The .38 Colt hollow base or .38 Long Colt heeled base bullet also works very well so as to compensate for the .375 measurement. The full .38 Colt may require a slight cutting down of the brass case due to the length of the bullet.

Another option is to get the barrel lined to .357. Lining the barrel to .357 will increase accuracy and any standard .38 caliber Long Colt bullet may be used.

Howell Conversions charges $85 to $100 for lining the barrel and you send the entire revolver to them including the conversion cylinder and the percussion cap cylinder as they will set the head space for the conversion cylinder and the cylinder gap for the cap & ball cylinder to assure a proper fit once the barrel is lined.