Could somebody explain +P ammo to me?

[chetrogers]

Im confused about the +P or the +p+ ammo that i see in stores.Im pretty new to Handguns and now that i have a few i am curious to know what it meens and if i should buy some for my hand guns.Im sure it matter on if youre handgun will be able to use it.I assume the + has something to do with the ammount of gun powder in the cartridge.But im confused i see it With +P and +P+.Thanks for any info on this.

Also i have a Smith and wesson .357 Highway patrol revolver and was curious if it would shoot the +p 38 special in it safely.I have already bough them but have not used them because i wasnt sure if it was safe.Thanks for your time.

 

[P95Carry]

Chet - +P is just fine in your M28. It is way below .357 levels.

+p is a tad higher pressure than ''normal'' ... +P+ of course tad higher still.

In 38spl ... +P should NOT be put thru a gun not marked as being acceptable for it. Equally with 9mm ... even more so in fact as this is a high pressure round anyways. Same for any other cal ... 45acp etc.

The ''std pressure'' round is best to stick to unless you know for sure that +P is OK. The ''P'' IIRC just stands for ''pressure''.

The change in loading (powder) can be very small - but enough to raise pressures beyond the std figures.

 

[chetrogers]

Thanks for the responce.Do you know if our P97's will take the higher loads.Thanks again.

 

[P95Carry]

Well, I know the P95 will digest +P just fine ... the P97? .... I'd have to check, as I have only ever used std loads. Someone else may know the answer.

I am thinking the answer is yes ... but still need to check to be sure. Someone else may have that answer.

 

[Phantom Warrior]

If I recall correctly, +P is loaded to a 10% higher pressure than the standard cartridge while +P+ is 15% higher. MOST modern guns are +P rated, but it is a good idea to check if you aren't sure.

 

[Preacherman]

The designations "+P" and "+P+" are in reference to the SAAMI maximum pressure levels for a given cartridge.

SAAMI (Sporting Arms & Ammunition Manufacturers Institute) sets a given pressure (usually measured in copper units of pressure, or CUP, although more modern systems are available) for any cartridge. You can see their pressure chart here.

Let's use .38 Special as an example of how pressures work. The SAAMI standard pressure for this round is 17,000 CUP. The .38 Special +P pressure is 18,500 CUP, or an increase of just over 8.8% from the standard .38 Special. There is no +P+ SAAMI specification - this simply indicates that the pressures of such a round exceed the +P specification (sometimes dangerously so, which is why SAAMI refuse to certify such pressures).

The reason for the pressures set by SAAMI is to ensure that the round in question can be safely fired in all, repeat, ALL firearms chambered for that round. Since many .38 Special firearms were made in the days of black powder, and were never certified for smokeless powder (let alone higher-than-usual pressures), the relatively low limit of 17,000 CUP set for this round ensures that any .38 Special firearm, even one made in the 19th Century, can fire any round meeting this specification. A modern firearm, in good condition, should not have any problems in shooting +P ammo. However, the use of +P+ ammo is "iffy", as even some modern firearms may not function properly with it, so your use of such ammo is at your own risk.

Hope this helps.

 

[HankB]

From what I've read, in 9mm P caliber, standard pressure ammo is limited to 35,000 PSI. "+P" ammo is 38,500 PSI. While there is no official "+P+" designation, I've bought some with a sticker on the box indicating they were loaded to 40,000 CUP. (These were major brands, not gun show reloads.)

Things get complicated as CUP units and PSI units can't be readily converted.

NATO ammo is pretty hot, too, but I believe there the pressures are measured via different techniques (Maybe according to European CIP standards?) and, again, there's no easy direct conversion to the more familiar SAAMI standards.

 

[dairycreek]

The assumption is that +p and +p+ gives you more velocity and energy!

But that is not necessarily true. It depends on how a particular round performs in a particular gun. I have chronographed some loads designated +p+ and found that they produced no more velocity (in a given bullet weight) that a "reguar" round did. Higher pressure loads will, however, produce higher operating pressure in a handgun. Over time, guns that operate at higher pressures will show increased wear - higher pressure does that.

It is not adviseable to shoot higher pressure loads in a particular handgun unless and until you find out if the gun was designed to do that. Call the manufacturer with the vital stats (serial number, etc) on the gun in question and ask about firing higher pressure loads in that particular gun.

 

[GlenJ]

I owned a Ruger P97 and +P is fine.

 

[BluesBear]

Things get complicated as CUP units and PSI units can't be readily converted.

yes and No.

Any valid Standardized Measurement Unit can be converted to any other SMU.
All you need to know is a valid formula. The problem with converting from CUP to PSI is that the commonly used method for measuring American CUP (ANSI) is NOT consistent.

The European (CIP) Copper Units of pressure measurement is done at the case mouth and can be VERY reliably converted.
The American (ANSI) Copper Units of Pressure is not as exact and therefore has a much larger margin of error.

So 40,000CUP (ANSI) would convert to between 42.732 and 45.732PSI

40,000CUP (ANSI) would translate into 9mm+P+
(note: that there is no SAAMI standard for 9mm+P+)
Which means that any ammo marked as +P+ is probably NOT loaded to SAAMI specifications.
The SAAMI specification for 9mm Winchester magnum is 45,000CUP (ANSI)


The only +P ammo recognized by SAAMI is .38 Special+P, 9mm Luger+P and .45 ACP+P.
Even though .38 Super is sometimes marked +P it is only +P when compared to .38ACP ammo.

Anything else that says +P is either loaded outside SAAMI specs or is just marketing hyperbole.

 

[unspellable]

pressure measurements

The modern pizzo transducer method measures the pressure directly and records the peak pressure as psi. As simple as that.

The CUP method relies on deforming a copper crusher and then comparing it to a tarage table. The problem is the tarage table is developed by putting static pressure on the crusher. In the actual test the peak pressure lasts for a very short time. Like any liquid, the copper has viscosity and requires time to flow. But it's not allowed sufficient time. Hence the CUP method will always give misleadingly low readings. There is NO way to convert to psi because we do not know how long the pressure was applied nor do the tarage tables contain any correction for short duration pressures. So no matter how much the accuracy is fine tuned there is an inherent error that cannopt be determined at the present state of the art. Probably never will be since evrybody is going to the pizzo method.