Defensive gun owners are always looking out for the right balance between power, accuracy, ammunition capacity and carrying weight in a handgun.
As a rule, an increase in caliber comes with a corresponding increase in the power of each shot, but this usually comes at the cost of some of the other factors.
A .40 S&W, for example, is more powerful than a 9mm, but it is also probably heavier, and you might have to come down by a few rounds in the magazine because of the ammunition’s larger size.
+P ammunition is one of the innovations that lets you max out on power without seriously affecting the other factors.
+P ammo is a standard handgun round that has a little more gunpowder in the cartridge than the typical ammo for a given gun.
This makes the round more powerful (hence the plus-P; the P is for power).
The extra kick is usually felt as additional recoil, but the rounds are the same size and dimensions as regular ammo, so no other gun modifications are necessary.
+P Ammunition History Lesson
On April 11, 1986, two people robbed a bank in Miami. The pair had done this several times before, and the FBI was trying to find them.
The pair had already killed or tried to kill several innocent people, and the heat was on to get them before their next robbery.
When an FBI agent spotted the pair near a bank in a stolen car, they tried to run. After crashing, the robbers got out, loaded for bear and blasted at the agents with a Mini-14.
A lot of words have been written about the 5-minute shootout that followed, including the script of a made for TV movie with Michael Gross (Stephen from Family Ties) and Jan Michael Vincent (Stringfellow Hawke, Airwolf), but the final FBI report on the incident was infuriating.
It turns out that the robber with the rifle got hit in the chest with a 9mm round early in the fight, maybe in the first 30 seconds of the shooting.
The bullet managed to pass through the robber’s arm, hit his chest, pass through a lung and stop half an inch from his heart.
Without medical care, this was probably fatal, but because the heart hadn’t been hit, the robber managed to keep fighting, eventually wounding five FBI agents and killing two.
Among the lessons learned from this shootout was that the standard-issue 9mm of 1986 was perhaps inadequate for its task.
That wasn’t true — the robber did die, just not right away, and the shot was probably a fluke — but the idea that 9mm wasn’t powerful caught on.
Ammunition suppliers went to the drawing board and came up with a few new ideas. One of these was the 10mm, which is kind of a Magnum round for automatics.
The FBI adopted this, but agents reportedly hated the round for its recoil.
In response to this, Smith & Wesson cut down their 10mm into a shorter round, which became the .40 S&W; the Depeche Mode of caliber choices.
All of this was in an effort to give law enforcement a slight edge in power that was felt to have been lacking that day in Miami.
+P Ammo
Meanwhile, the makers of 9mm ammo (basically every company that makes handgun ammo) were working on their own solution.
Rather than reinventing the wheel and forcing everybody to buy new guns for bigger rounds, developers were experimenting with putting larger quantities of powder inside the standard 9mm cartridge.
Developments in metallurgy and case design made it easier to build an overpressured cartridge that wouldn’t crack with the extra force of the +P load.
The round was broadly popular in 9mm, and so it wasn’t long before +P ammo was available for other calibers as well.
In 2020, +P options are common in these calibers as well
- .257 Roberts
- .38 Special
- .38 ACP
- .45 ACP
The +P concept adds a lot to each of these rounds.
The .38 Special +P — not to be confused with the .38 Super, which is the +P .38 ACP round — provides a round of intermediate power between the standard .38 Special and the .357 Magnum, which can have a bit too much snap for short-barreled revolvers.
The .257 Roberts +P round kicks the projectile extra fast and makes for a very flat trajectory and improved accuracy at range.
And +P in the .45 ACP round helps the 230-grain bullet move somewhat faster than a scared house cat, which is a nice change of pace for 1911 shooters.
Not an Exact Science
It’s worth remembering that +P is not a technical term but rather a marketing one.
There isn’t a controlling authority that regulates what is and is not +P, so the enhanced power of these rounds is all over the map.
The Sporting Arms and Ammunition Manufacturers' Institute (SAAMI), which helpfully tests ammo for consumers, estimates that +P adds around 10% to the power of a 9mm round, while the .257 Roberts only gets 7.41% extra.
The .45 ACP goes up around 9.5% in +P, while the .38 Super earns its name with a massive 37.75% increase over the standard .38 ACP you bought for some reason 25 years ago.
These outputs are not even close to standardized, and if you get into +P+ ammo you’ll find even more variation on the high end.
It’s worth noting that +P is almost always less powerful than the Magnum ammo that might be available in the same caliber, and it’s only around half the pressure inside the chamber as the proof round they shot through your gun at the factory to make sure it wouldn’t blow up on you.
Speaking of which. . .
Safety Concerns
It goes without saying that guns go bang, and when that bang is more than they can handle, you might have a safety issue on your hands.
It’s easy to exaggerate the risks here, since basically all modern guns (i.e. made after 1990 or so) are able to handle the +P version of whatever they shoot.
Check the ammo rating stamped into the barrel if you aren’t sure, or consult the operator manual for a definitive list of the ammunition your gun can safely shoot.
The real danger of shooting +P through an old gun isn’t that it will explode into a mushroom cloud on you — much more likely is that it’ll damage the gun’s internals.
When you load a round into the chamber, the nose of the bullet is pointing at a metal ring called the forcing cone.
These are pretty tough today, but in the past, they tended to get made out of softer steel.
Consistently shooting +P through the barrel of an older gun might eventually cause your forcing cone to distort, since there’s more pressure hitting it than it was designed for.
This eventually causes failure to feed malfunctions and could even obstruct the barrel.
If you’re ever in doubt about what you can shoot, don’t be shy about asking a gunsmith to have a look at your gun.
