There are truly many mysteries to unravel in the world of firearms and shooting sports, especially for those interested in personal, home and family self-defense. One major source of confusion revolves around types of ammunition. Here we’ll focus on one particular aspect: what is overpressure, or +P and +P+, ammunition?
What Is Overpressure Ammo?
Overpressure ammunition — often designated as +P or +P+ ammo depending on the type and brand is actually one of the simplest ammunition/caliber concepts to explain.
All American ammunition, as well as foreign-manufactured ammunition sold in the U.S., must adhere to safety standards and specifications set by Sporting Arms and Ammunition Manufacturers Institute (SAAMI), an organization that has been around since 1926.
SAAMI establishes all the rules regarding cartridge dimensions and operating pressures, among other things. Cartridges are required to pass SAAMI tests and standards, which include generating safe chamber pressures. These standards ensure consumers who load their firearms with the correct type and caliber of ammunition won’t face catastrophic failures when firing.
Each caliber/cartridge has a standard operating pressure known as “standard pressure.” This pressure can vary depending on multiple factors, such as the introduction date of the cartridge. For example, the standard operating pressure of a .38 Special revolver cartridge (introduced in 1898) is much lower than that of the .357 Magnum (introduced in 1935). The lower pressure of .38 Special cartridges is meant to protect individuals using older .38 Special revolvers. As metallurgy improved over time, +P and +P+ ammunition were developed to enhance the effectiveness of these chamberings. +P ammo can be identified by specific markings on the box and cartridge case rim.
+P Ammunition in Self-Defense Shooting
While the 9mm and .45 ACP are also available in +P loadings, there are no +P loadings available in .357 Magnum. This cartridge is already powerful enough without increasing pressure. (Buffalo Bore does offer a +P .40.) However, for the purpose of this article, I will focus on the .38 Special revolver cartridge, as it was the first +P caliber I ever worked with.
When I started with the Licking County, Ohio, Sheriff’s Office in 1980 as a reserve Deputy Sheriff, I chose to carry a Model 19 Smith & Wesson .357 Magnum revolver loaded with .38 Special ammunition as my duty handgun. At the time, two popular duty loads were +P loadings: the Speer Lawman 125-grain .38 Special JHP and the 95 grain Winchester Silvertip .38 Special JHP.
The Evolution of +P Loads
Four years later, while working full-time as a police patrolman for the City of Reynoldsburg, Ohio, I was introduced to two newer +P .38 Special loads. Both were from Winchester and were making waves in the world of police revolvers
The Winchester +P 158-grain Lead Semi-Wadcutter Hollow-Point (LSWCHP) was our duty load at Reynoldsburg for duty and off-duty revolvers. Known as the “FBI Load,” the LSWCHP bullet combined the sharp shoulder and flat nose of a semi-wadcutter bullet, which tends to cut into blood vessels it passes rather than just push them aside, with a plain lead hollow-point for added expansion. This +P loading has a relatively low blast signature. It left the muzzle of a 4-inch revolver barrel at 890 feet per second and delivered 278 foot-pounds of energy at the muzzle. While these ballistics seem rather tame by today’s +P standards, it gave the shooter an additional 100 feet per second velocity over standard pressure 158-grain .38 Special loads. It was controllable but still effective, and several agencies in my area issued it.
For many years, S&W five-shot J-Frame revolvers were not rated for +P ammo. However, I first carried this load in the nickel-plated Smith & Wesson Model 10 .38 Special revolvers we were issued. When we were later issued Smith & Wesson Model 65 .357 Magnum revolvers, any concerns over using +P ammunition were eliminated. The larger six-shot K-frame revolvers could handle the use of relatively mild +P Winchester 158-grain LSWCHP load.
However, Colt’s original D-Frame six-shot snubs could. The all-steel Detective Special was rated to use up to 2,000 rounds of +P ammo before needing inspection at the factory. The aluminum-framed Agents and Cobras were rated for 1,000 rounds before inspection was needed. As metallurgy improved, the round limitation for +P ammo was eliminated. As well, all Smith & Wesson J-Frame .38 Special revolvers are rated for +P ammunition today.
+P+ Ammo
The competing overpressure .38 Special load in my area was also produced by Winchester. Known as the “Treasury Load,” it was for law enforcement use only and marked “not for retail sale.” It was the only +P+ — double overpressure — load of the time. The Winchester +P+ 110-Grain JHP load is still being manufactured by Winchester and is still for law enforcement use only. Its bullet leaves the muzzle at 1,155 feet per second and delivers an impressive 326 foot-pounds of energy, which can be wearing on certain firearms.
Winchester’s +P+ ammo differs significantly from +P ammo. The warning on the back of the box is comprehensive, stating that these cartridges adhere to the higher velocity and pressure specifications set by the U.S. Treasury Department, which surpass conventional .38 Special cartridges. The ammunition is capable of causing permanent damage to aluminum or lightweight frame revolvers. The maximum average pressure is approximately 15-20 percent higher than the industry’s +P standard, which equates to around 23,500 Copper Units of Pressure. Essentially, Winchester cautions that this .38 Special ammunition approached the power of a low .357 Magnum. It is unclear why the Treasury Department didn’t simply issue .357 Magnum revolvers loaded with middle-range ammunition instead of creating a potentially hazardous situation with the +P+ round.
Using +P Ammo in Your Concealed Carry Gun
- Always check the box of .38 Special, 9mm, .40 or .45 ammo, as well as the cartridge cases, for +P ratings stamped on the bottom of the box and cartridge case rim before loading or shooting.
2. Ensure your handgun is rated for +P ammo use.
3. Remember that any .357 Magnum, regardless of weight, can safely handle any +P or +P+ ammo. Both loads are less powerful than the .357 Magnum round.
4. Stick to using standard velocity ammo with any handgun or rifle that is not marked to accommodate +P .38 ammo.
5. While it is unlikely for a duty-quality .38 Special revolver to explode when firing 110-grain Winchester +P+ .38 Special ammo, it is best to reserve such rounds (if available) for use in revolvers chambered for the significantly more powerful .357 Magnum cartridge. The same applies to J-frame .357 Magnums.
6. Self-defense ammunition doesn’t necessarily need to be +P loaded to be effective. Thanks to advancements in modern smokeless powders and improved bullet designs, enhanced bullet performance can be achieved without the need for +P or +P+ pressures. For example, Liberty Ammunition offers various self-defense loads that are not loaded to +P levels, although some of their loads are. Winchester also offers two Silvertip self-defense loadings in 9mm — 115-grain and 147-grain — that do not carry the +P rating.
Using +P and +P+ Ammunition for Self-Defense
It is crucial to be aware of the differences between +P and +P+ ammo and to exercise caution when using them. Always follow the guidelines provided by the manufacturer and ensure your firearm is suitable for such ammunition. +P and sometimes +P+ ammo have their place in the world of defensive firearms. I carry +P in my handgun whenever hiking in big bear country, for example.
In the end, +P ammo delivers more recoil and blast than standard-pressure loads, whether for rifle or handgun rounds. They also tend to be a bit more expensive than standard-pressure rounds. I recommend that if you want to carry +P loads, first make sure your handgun can handle that type of load. Your gun’s owner’s manual will tell you what type of ammunition is suitable for it. If it’s a +P-rated gun, buy a small amount of defensive ammo to test fire first. If you can fire it accurately with one and two hands, then go for it. You may find that the additional up-front action is not worth it for you. Find a quality standard-pressure load that you like instead. To paraphrase Wyatt Earp: “Power is fine, but accuracy is final. You have to deliver accurate shots to stop a threat.”
For more in-depth information on handgun, rifle, and shotgun cartridges, consider picking up a copy of Gun Digest’s “Cartridges of the World.” This comprehensive resource can help unravel many of the mysteries about American and European ammunition.
Sources
Gun Digest: GunDigest.com
Liberty Ammunition: LibertyAmmo.com
Winchester: Winchester.com
