"+P" is an official SAAMI designation for ammunition loaded to higher than normal maximum average pressure (MAP) and thus higher than normal velocity. The purpose is to increase the effectiveness of standard calibers, such as the .38 Special, 9x19mm and .45 ACP. This article is about SAAMI specification +P ammunition that is available to civilian shooters.

"+P+," on the other hand, is an unofficial designation used by some manufacturers for ammunition loaded to higher than +P pressure. Such loads are usually intended for use by law enforcement agencies.

Of course, there is a limit to how much the MAP can safely be increased, as there is a limit to the strength of the handguns available in these calibers. They are not magnums and cannot withstand the pressure generated by magnum cartridges.

Each caliber for which +P ammunition is available has its own standard MAP and +P MAP specification. 9x19mm +P cartridges, for example, are loaded to a different MAP than .38 Special +P cartridges.

+P ammunition is headstamped accordingly, for example ".38 Spec. +P." +P loads should be fired ONLY in firearms specifically designated by the manufacturer as suitable for this elevated pressure ammunition. Such firearms should be identified by the caliber marking on the barrel and the owner's manual supplied with the gun should clearly state its suitability for use with +P ammunition.

The most commonly encountered +P handgun calibers are .38 Special, 9x19mm (9mm Luger), .38 Super Automatic and .45 ACP. SAAMI has established +P pressure levels for these cartridges and factory loaded +P ammunition is available from the major U.S. ammo companies (Remington, Winchester, Federal and Hornady). Here are the standard and +P MAP's for these cartridges:

• .38 Special: 17,000 psi (std.); 20,000 psi (+P) = 17% increase in pressure
• 9x19mm: 35,000 psi (std.); 38,500 psi (+P) = 10% increase in pressure
• .38 ACP/.38 Super: 26,500 psi (.38 ACP); 36,500 psi (.38 Super +P) = 38% increase in pressure
• .45 ACP: 21,000 psi (std.); 23,000 psi (+P) = 9.5% increase in pressure

In the Beginning: the .38 Special High Velocity and .38 Super Automatic

Historically, the +P designation grew out of the experiments conducted by American ammunition manufacturers during the late 1920's with high velocity .38 Special loads. The 1930's saw ammo makers market high pressure .38 Special loads that were intended for use ONLY in large frame revolvers, principally the .44 frame size double action revolvers then produced by Colt (New Service) and Smith & Wesson (N-frame).

These factory loads were marked "High Velocity," "High Speed," or ".38/44" on the box, but customers persisted in shooting them in medium frame revolvers (Colt D-frame and S&W K-frame), with the potential for damaged or blown-up guns and injured shooters. Eventually, the High Speed .38/44 factory loads were discontinued and, in 1974, replaced by (less violent) .38 Special +P ammunition. Note that to allow +P ammo to be used in medium frame revolvers, it is loaded to lower velocity than the earlier High Speed .38/44 loads.

Remington and Winchester catalog figures from 1966 for their High Velocity .38/44 loads call for a 158 grain lead bullet at a muzzle velocity (MV) of 1090 fps and muzzle energy (ME) of 425 ft. lbs. from a 6" test barrel. Remington and Winchester 2011 catalog figures for their .38 Spec. +P loads show a 158 grain lead bullet at a MV of 890 fps and ME of 278 ft. lbs. from a 4" test barrel.

Standard SAAMI specification .38 Special ammunition is loaded to a MAP of 17,000 psi, while .38 Special +P ammunition can be loaded to a MAP of 20,000 psi. As you can see, .38 +P ammo is loaded to about 17% higher pressure than standard loads. This is a significant, but not dramatic, improvement. For comparison, the SAAMI limit for the .357 Magnum (based on a .38 Special case lengthened by 0.135" to prevent chambering in .38 revolvers) is 35,000 psi.

Another cartridge developed before the standardization of the +P designation is the .38 Super Automatic. The forerunner of the .38 Super was the .38 Auto (.38 ACP), which was introduced in 1900. The .38 Auto was one of the early smokeless powder cartridges developed for autoloading pistols. It was offered in the Colt .38 Automatic Pistol and it drove a 130 grain bullet at a MV of 1050 fps. The actual bullet diameter was .355", the same as the 9mm Luger cartridge. The production of .38 Auto pistols ceased in 1928. The .38 Auto cartridge is obsolete and has not been factory loaded for many years.

In 1929, Colt introduced an over-pressure version of their .38 Automatic cartridge in the stronger Model 1911 pistol, which they dubbed the .38 Super Automatic. The .38 Super cartridge is dimensionally identical to the .38 ACP, but loaded to higher pressure. The .38 Super Auto achieved a MV of 1280 fps with the same 130 grain bullet. For many years it was the most powerful cartridge available in autoloading pistols. The .38 Super became moderately popular and remains available today.

When the +P cartridge designation was adopted in 1974, it was tacked onto the .38 Super, although the long established SAAMI pressure limit for the .38 Super was not changed. In this case, the +P designation means "higher pressure than the .38 ACP cartridge." All .38 Super ammunition has always been loaded to higher pressure than .38 ACP ammo.

Modern +P Velocity Comparison

The benefit from increasing the MAP of +P cartridges is increased MV and potentially greater stopping power. These are, after all, handgun cartridges commonly used for self-defense. Here are some velocity comparisons of standard pressure and +P loads (based on Remington and Winchester data):

• .38 Special: 125 grain bullet at 850 fps
• .38 Special +P: 125 grain bullet at 945 fps
• 9x19mm: 124 grain bullet at 1140 fps
• 9x19mm +P: 124 grain bullet at 1200 fps
• .38 ACP: 130 grain bullet at 1050 fps
• .38 Super +P: 130 grain bullet at 1280 fps
• .45 ACP: 185 grain bullet at 1015 fps
• .45 ACP +P: 185 grain bullet at 1140 fps

The velocity gain for the modern .38 Special, 9x19mm and .45 ACP +P cartridges shown here varies between 60 fps and 125 fps. At 95 fps, the .38 Special's +P velocity gain puts it somewhere in the middle of the range.

+P Stopping Power Comparison

How effective is +P ammo on the street, compared to standard pressure loads? Here are some comparisons based on the stopping power data compiled by Marshall and Sanow in Handgun Stopping Power. In the list below, the "one shot stop" percentage (rounded off to the nearest whole number) for a standard pressure load is followed by the percentage for a +P load from the same manufacturer using the same weight bullet.

• .38 Special = 53% (Federal 158 grain LSWC)
• .38 Special +P = 74% (Federal 158 grain LHP)
• 9x19mm = 80% (Winchester 115 grain Silvertip JHP)
• 9x19mm +P = 89% (Winchester 115 grain JHP)
• .45 ACP = 80% (Remington 185 grain JHP)
• .45 ACP +P = 86% (Remington 185 grain JHP)

The biggest +P increase shown here is for the .38 Special (21 percentage points). However, this is primarily due to the difference in bullet construction, rather than the difference in velocity.

Marshall and Sanow only provided stopping power numbers for a limited number of loads and I had to compare what was available. The standard pressure Federal load shown above used a lead semi-wadcutter bullet that typically shows little or no expansion after impact, while the +P Federal load used a more terminally effective lead hollow point bullet that usually expands after impact.

Superior JHP bullets are available in .38 Special loads and the top .38 "stopper" recorded by Marshall and Sanow, at 83%, was the Cor-Bon +P load using a 115 grain JHP bullet. Unfortunately, there was no equivalent standard pressure load available for comparison.

The 9mm and .45 loads shown above all used jacketed hollow point bullets with similar terminal performance, which minimized the difference between the standard and +P loads. When standard and +P loads using similar JHP bullets are compared, the improvement in one shot stops provided by the +P ammunition shown above was 6% to 9%, a worthwhile, but not overwhelming, advantage.

Non-standard "+P" Ammunition

How about the "+P" cartridges for calibers such as the .32 ACP and .380 ACP that are offered by some specialty ammo makers, such as Buffalo Bore? The answer, as far as I can determine, is that there are no SAAMI standards for +P ammunition in these calibers.

Ammunition so labeled is not true +P. It is either loaded to the standard SAAMI MAP for the cartridge (perhaps right at the upper limit), or loaded to higher than permissible (thus potentially dangerous) pressure. The former is a marketing gimmick to stimulate sales and the latter (over-pressure loads) are not safe for use in all guns and may degrade your pistol's reliability and longevity.

Almost all .32 ACP and .380 ACP semi-automatic pistols are blow-back operated, not locked breech designs. In these pistols only the mass/inertia of the breech bolt and the pressure of the recoil spring keep the action closed during firing. These are carefully calibrated to the anticipated pressure of the cartridge for which the pistol is chambered. Any increase (or decrease) in the cartridge's MAP can create an unsafe and/or unreliable condition.

In other words, these cartridges are intended to be loaded within a narrow range of pressures that cannot be exceeded if the guns designed to shoot them are to operate correctly. Since any handgun used for personal protection must, above all, be reliable, I recommend against the use of ersatz "+P" ammunition. Stick with ammunition loaded to SAAMI specifications.

A different situation is represented by hot .45 Long Colt revolver loads, such as the Cor-Bon .45 Colt +P, which Cor-Bon clearly states is not loaded within the SAAMI pressure limit for the .45 Colt cartridge. This over-pressure ammunition is equivalent to the loads listed in most reloading manuals that are intended for use ONLY in Ruger Blackhawk and T/C Contender pistols.

These loads are unsafe in other .45 Colt revolvers and specifically should not be fired in S&W N-frame revolvers, Colt Single Action Army (P-frame) revolvers or copies of such. The SAAMI standard MAP for the .45 Colt is 14,000 psi and .45 Colt +P ammunition is reportedly loaded to about 27,500 psi, a 97.4% increase in pressure! At almost double the standard pressure, these .45 Colt +P loads are far in excess of even the heaviest proof loads and are likely to destroy guns not specifically designed to handle them.

Conclusion

Compared to standard pressure loads, +P ammunition generally provides a useful increase in velocity and stopping power. The difference is much less than between standard and magnum calibers, but it is real. There is also an attendant increase in muzzle blast and recoil, but it is usually moderate.

Conversely, the improvement is not so great as to make +P ammunition mandatory for successful personal defense. In particular, handguns designed only for standard pressure ammunition should not be fed +P loads.

The limited performance advantage offered by using +P ammunition is more than offset by the attendant decrease in reliability and the potential for gun damage. Self-defense firearms must be as close to 100% reliable as possible. A gun that malfunctions may get you killed. Gaining a few percentage points in theoretical stopping power is certainly not worth the risk of catastrophic failure in a life and death situation. By far, the most important factor in stopping power is bullet placement, not cartridge power.