A new-to-me term I'm seeing: +P ??

I'm familiar with +P pistol cartridges/loading. Is it the same connotation for rifle cartridges? And a secondary question: if a "book load" is listed as having low pressure but the "fastest" comparitive velocity and listed as a maximum load, does that mean there is room to +P it??
Example from XXL Reloading: 30 Nosler, Hornady GMX 180gr, 78.2gr Winchester Staball
97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum. I don't get it?!?

8x68s said:

I'm familiar with +P pistol cartridges/loading. Is it the same connotation for rifle cartridges? And a secondary question: if a "book load" is listed as having low pressure but the "fastest" comparitive velocity and listed as a maximum load, does that mean there is room to +P it??
Example from XXL Reloading: 30 Nosler, Hornady GMX 180gr, 78.2gr Winchester Staball
97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum. I don't get it?!?

Click to expand...

If you are referring to the +P throating, it was pioneered by Shawn (https://defensiveedge.net/) a few years ago. It is not for everybody, but consult with him directly if your setup is worth your investment. Good luck!

People are referring to Federal's steel cases running at 80kpsi as +p in rifles. Pistols with +p are generally also over pressure.

I really doubt anyone on XXL reloading has a pressure trace so take any pressure claims with a massive heaping of salt.

+P only means it is loaded higher than standard SAAMI pressure.
Many older cartridges were loaded to lower chamber pressures ie, 7x57, 8x57, 257 Roberts and 38 Super.
Due to SAAMI listed maximum chamber pressures, if an ammo company wants to load ammo higher than this, it must have the +P designation so that it is not fired in old guns, although this is probably not going to happen these days. Speer listed +P load data before anyone else for 257 Roberts.

Cheers.

8x68s said:

I'm familiar with +P pistol cartridges/loading. Is it the same connotation for rifle cartridges? And a secondary question: if a "book load" is listed as having low pressure but the "fastest" comparitive velocity and listed as a maximum load, does that mean there is room to +P it??
Example from XXL Reloading: 30 Nosler, Hornady GMX 180gr, 78.2gr Winchester Staball
97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum. I don't get it?!?

Click to expand...

OOPS, my bad, I locked into the +P, instead of your example. For some reason, I do not have the option to edit my post. The dropdown menu on bottom left corner was non-existent.

8x68s said:

97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum. I don't get it?!?

Click to expand...

This is the problem here, due to the methods of SAAMI measuring devices and THEIR stupid rules, you may have 10 loads that all measure with an average MAP (Max Average Pressure) below the listed maximum, BUT, some years ago now, they dropped MAP to MP (Maximum Pressure) which means that no load out of the 10 loads tested can exceed MP, not an average, just ONE and that means that load is unsafe.
Now, we all know that even with identical powder charges, no 2 loads perform exactly the same, some get very close, but, rarely identical.
So, why did SAAMI move away from averages to absolute measurements? I have never got a direct answer, although
I have used their reference ammo in the past. Even their fudge factor changed from an average to an absolute, it makes no sense.

Cheers.

MagnumManiac said:

This is the problem here, due to the methods of SAAMI measuring devices and THEIR stupid rules, you may have 10 loads that all measure with an average MAP (Max Average Pressure) below the listed maximum, BUT, some years ago now, they dropped MAP to MP (Maximum Pressure) which means that no load out of the 10 loads tested can exceed MP, not an average, just ONE and that means that load is unsafe.
Now, we all know that even with identical powder charges, no 2 loads perform exactly the same, some get very close, but, rarely identical.
So, why did SAAMI move away from averages to absolute measurements? I have never got a direct answer, although
I have used their reference ammo in the past. Even their fudge factor changed from an average to an absolute, it makes no sense.

Cheers.

Click to expand...

Lawyers……

So, back to the example:
97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum.

#1... So, theoretically, if this case could pack more powder to achieve something closer to max pressure it would still be a safe load... and NOT +P.
#2... Would it be more efficient to use a different powder with a similar fill % and higher resulting pressure?

I would think, as in the example, if the powder gets the sought after velocity, the lower pressure is going to be much easier on the rifle...

akmtnhnt said:

People are referring to Federal's steel cases running at 80kpsi as +p in rifles. Pistols with +p are generally also over pressure.

Click to expand...

Good info. Would anyone be able to reload steel cases fired at 80Kpsi?
I would think they would be spent with a single firing (like factory WSSM ammo).

Mikecr said:

Good info. Would anyone be able to reload steel cases fired at 80Kpsi?
I would think they would be spent with a single firing (like factory WSSM ammo).

Click to expand...

They say yes, and it' been shown to be done, but I don't think many people have yet.

8x68s said:

So, back to the example:
97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum.

#1... So, theoretically, if this case could pack more powder to achieve something closer to max pressure it would still be a safe load... and NOT +P.
#2... Would it be more efficient to use a different powder with a similar fill % and higher resulting pressure?

I would think, as in the example, if the powder gets the sought after velocity, the lower pressure is going to be much easier on the rifle...

Click to expand...

I tried to explain this earlier, if the next step-up in powder charge produces ONE test round that is over max pressure, that load is deemed dangerous and is not used.
And yes, 1 additional grain of powder can cause this.

Is the load you're referring to from a published +P load data source? I don't know who XXL is.

Cheers.

XXL is a European based (German??) website that publishes cartridge reloading data. I have used it for some odd or Euro-typical cartridges I use and to extrapolate for wildcats cartridges I have developed. You might give it a look. It has been very helpful in providing info on cartridges that don't show up in reloading manuals as well as info on common cartridges. It is definitely not a +P oriented website. In fact, I have found a lot of their listed loads to be somewhat conservative.

Ok, so, if the load you mention is 73% of max, which we don't know whose max, could be CIP, then adding powder beyond that level may, or may not, bypass maximum pressure.
Unless you can test this, I wouldn't be guessing.
With my 7x68 wildcat, which I have not used in more than 10 years, I did all my testing with a Pressure Trace II in conjunction with QL using CIP parameters from the parent case.
Finding data outside of QL was non-existent. I ran the numbers up to 65,000psi, the RWS brass held up very well to these pressures, but, I felt lowering the pressure back to 60,000psi was nicer on the brass. Obtaining more RWS brass is not possible here anymore and too costly to do for even 200 pieces.
Any +P loading should be tested, as pressure rises fast after about 70,000psi. It is not linear either, it can jump to 100,000psi with a small increase in the wrong powder.

Cheers.

8x68s said:

I'm familiar with +P pistol cartridges/loading. Is it the same connotation for rifle cartridges? And a secondary question: if a "book load" is listed as having low pressure but the "fastest" comparitive velocity and listed as a maximum load, does that mean there is room to +P it??
Example from XXL Reloading: 30 Nosler, Hornady GMX 180gr, 78.2gr Winchester Staball
97% case fill, velocity of 2953fps, 47.5k pressure which is only 73% of maximum. I don't get it?!?

Click to expand...

Perhaps this will help you understand a little better how it works. Cheer's

Standard pressure, +P, and +P+ refer to different pressure levels for handgun ammunition, as defined or recognized by organizations like SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) in the U.S.

Key Concepts
- **Standard (SAAMI max average pressure)**: The safe, published pressure limit for factory ammunition in standard firearms.
- **+P**: Higher-pressure ammunition (still within SAAMI guidelines for many cartridges) for increased velocity/energy. It requires firearms rated for +P use. Not all guns (especially older or compact ones) are approved for it.
- **+P+**: An unofficial, even hotter loading beyond SAAMI +P specs. It is **not standardized by SAAMI** and carries higher risk of damage or injury. Many manufacturers advise against it except in specific tested firearms.

Pressures are typically measured in **psi (pounds per square inch)** using SAAMI or C.I.P. methods (piezo or copper crusher). Actual pressures can vary slightly by load, bullet weight, and testing method.

Examples by Common Caliber

**9mm Luger (9x19mm)**
- **Standard**: 35,000 psi (SAAMI maximum average pressure)
- **+P**: 38,500 psi (SAAMI)
- **+P+**: Often 40,000–42,000+ psi (non-standard; examples from some specialty loads)

This is one of the most common examples where +P is widely available and many modern pistols are rated for it.

**.45 ACP**
- **Standard**: 21,000 psi (SAAMI)
- **+P**: 23,000 psi (SAAMI)
- **+P+**: Typically 25,000+ psi (unofficial)

.45 ACP +P is common for defensive loads, but +P+ is rarer and more stressful on the gun.

**.38 Special**
- **Standard**: 17,000 psi (SAAMI for standard pressure loads)
- **+P**: 18,500 psi (SAAMI)
- **+P+**: Often 20,000+ psi (unofficial; common in some +P+ .38 loads)

Note: Many .38 Special revolvers (especially older ones) are **not** +P rated.

**.357 Magnum** (for comparison)
- Standard pressures are already high (~35,000–40,000+ psi depending on load). +P/+P+ designations are less commonly applied here, as it's inherently a high-pressure cartridge.

Important Safety Notes
- Always check your firearm manufacturer's manual for +P or +P+ approval. Using higher-pressure ammo in non-rated guns can cause malfunctions, accelerated wear, or catastrophic failure.
- +P+ ammo is often marketed for law enforcement or extreme defensive use but increases recoil and reduces component life.
- Pressures are **maximum average**; individual rounds can peak higher. Chronograph testing and proper reloading data (if handloading) are essential.

These are general representative values based on industry standards. Exact specs can vary slightly by source or specific cartridge variant. For the most precise/current data, consult SAAMI publications or the ammunition manufacturer's technical sheets.