Trigger Talk March 2014 article: Making sense of calibers
It is easy to forget that our gun jargon can be confusing to new shooters concerning caliber names and designations.
This is especially true for the .380 acp, .38 special, 38 Super, .357 Magnum, .357 Sig, 9mm, and about a dozen more all of which have virtually the same diameter. The projectile diameter for these rounds all range between .355 and .357 of an inch, just 2 thousandths (.002) of an inch apart.
The difference is in the length of brass, and the amount and type of propellant. There are also rounds called 38 Smith & Wesson and 38 Smith & Wesson Long and a few thrown in called .38 Colt Police and .38 Long Police which are the same but Colt Arms did not want to stamp Smith & Wesson on their revolvers so they came up with their own Colt cartridge name.
9mm X 19 is a metric designation which means (the diameter of the projectile) X (the length of the case), in some cases the exact same round as the English Caliber.
A few examples:
.380 acp (Automatic Colt Pistol) = 9mm X 17mm is the same the metric designation and can also be named the 9mm Kurtz or Short
9X18 = 9mm Makorov which is a Russian round
9X19 = 9mm Luger or 9mm Parabellum
9X20 = 9mm Browning Long.
9X21R = 38 Special
9X23 Largo
In the 1930’s the .38 Special was commonly used for Police work, often needing to shoot gangsters through car doors. They made it more powerful by adding more propellant or changing the burn rate.
A typical pressure in the fired chamber of a .38 Special is about 17,000 PSI (pounds per square inch). The new .357 Magnum increased the pressure to 35,000 PSI resulting in what was called at the time “The most powerful handgun in the World”.
This created a problem since the case diameter was the same as a .38 special. They didn’t want people to put the new more powerful round into older guns made for lower pressures, which could literally blow the gun up! The solution was to lengthen the case about an 1/8 inch so it could not fit in the cylinders of a 38 Specials and the .357 Magnum was born.
Designed for higher pressures a .357 Magnum gun can safely shoot the shorter .38 Special at its lower pressure and the round will fit in the cylinder. This same “Special versus Magnum” designation is used for some larger calibers such as .44 Special and .44 Magnum.
Modern metallurgy has gotten better and today’s 38 special revolvers are capable of taking higher pressures than those made 75-100 years ago. The caliber of a revolver is always stamped on the barrel, and in past 40 years you see many with .38 Special +P, this stands for “Plus Pressure”. I mentioned earlier that a typical 38 Special is loaded to approx. 17,000 PSI, while a 38+P round will be loaded to 20,000 PSI.
Popular for self-defense, many people use +P rounds in short barreled revolvers because the higher pressure helps make up for loss of velocity with a short barrel. The higher velocities are necessary to ensure proper expansion of hollow-point ammunition
If you are unsure of your guns ability to fire +P rounds, and it is not printed on the barrel, contact the customer service department of the gun manufacturer and they can tell you if it was designed for +P pressures.
Also available for semi-auto pistols, +P rounds, if you plan to use them you should fire a few boxes to ensure your pistol will function properly and to get used to the higher recoil. There is no reason to spend extra money on +P’s for target shooting or practice.