[k say]

what does this term mean +p or +P+ pls.

[ChristopherG]

They refer to elevated levels of pressure to which a cartridge in a given caliber may be loaded. So a regular .38 special, e.g., has a maximum pressure (when ignited) of something like 16,500 C.U.P. (some unit of pressure, I don't know what exactly). A 38+p, though, can be loaded to around 18,500 C.U.P. (and consequently more velocity, but not in a straight line correspondence). These standards are set by SAAMI, an industry regulating board. They are set so that everyone will know if their gun is strong enough to take a given ammunition safely. Some revolvers, for instance, are 'rated' as safe to fire .38+p; others (mostly older ones) aren't.

+P+, on the other hand, is an Unofficial way to designate a load that exceeds even +P standards; it tells you it exceeds any SAAMI standard, but doesn't tell you by how much. Potentially dangerous, though not necessarily. Elmer Keith developed some famous loads in .44 special that were decidedly +p+, and became, eventually, the precursor of the .44 magnum. He did the same thing with the .38, leading to the .357 magnum. So it can be pioneering; but then, it can also be stupid. Probably only in retrospect is it easy to see which a given case will be.

Wiser minds may correct some of this, but that's the jist, I'm confident.

[Standing Wolf]

C.U.P. stands for "copper units of pressure." It has something to do with compressing copper in test barrels. Frankly, I've never understood why pressure isn't expressed in pounds per square inch.

Anyone?

[Gordon]

Pressures ARE beginning to be expressed in PSI. The Oehler Lab strain guage is calibrated in this. I have found 45,000Cup rounds normally are a little over 50,000 PSI . And 53,000CUP rounds are 60,000PSI +!:)

[Jim Watson]

It is. Expressed in psi, that is.

History:

The long time standard chamber pressure gauge was a barrel with a hole drilled in the chamber, a steel piston in the hole, and a strong clamp holding a little copper cylinder, the "crusher", against the piston. Fire the shot, the chamber pressure squashes the copper cylinder. Measure how much shorter is is and look on the "tarage table" to see how much pressure it took by dead weight or hydraulic pressure to shorten a sample of cylinders from that batch by that amount. That load, in psi, was recorded as the chamber pressure.

Time moved on, electronics got involved. The usual pressure gun now has a quartz piezoelectric transducer in a socket over the chamber. Firing the shot generates an electric impulse that can be calibrated against standard powder loads or hydraulic pressure. The display is set up to read out directly in psi.

But there were still some copper crusher guns in use, and the operators noticed that the readings were not the same. Mostly because the quartz transducer has an electronically fast response, and is reading pretty close to the actual peak pressure; but the crusher, being a chunk of metal, takes time and energy to deform. By the time it does, the pressure has peaked and fallen back off. The fast moving chamber pressure is going to peak out higher than what the crushers' calibration on a static press showed. So the industry agreed to rename pressure readings by crusher gauge CUPs for Copper Units of Pressure (shotgun shells in Lead Units of Pressure, LUPs, because they used softer lead crushers to get a better handle on the lower pressures.) Transducer readings are considered to be "real" pressure and are given in psi.

The values are not the same and there is no reliable conversion factor. You have to go with the data given, a maximum load is maximum.

Euro CIP pressure readings are slightly different from US SAAMI readings, the crusher port or transducer are at the case mouth, not over the chamber wall.

The British do it still differently, the crusher is in the bolt and measures the axial pressure. They are rated in "tons per square inch." And it gets more complex from there, readings are really not interchangeable or convertible.

[PaulS]

To show how CUP and PSI readings differ from round to round here is a table that I am compiling:



Cartridge SAAMI Pressure (PSI) SAAMI Pressure (CUP)

25 Auto 25000
32 Auto 20500
32 S&W Long 15000
32 H&R Magnum 21000 CUP
32-20 Winchester 16000 CUP
380 Auto 21500
9x18mm Makarov 24100
9mm Luger 35000
357 Sig 40000
9mm Largo 30000
9x23mm Winchester
38 ACP
38 Super (+P) 33000 CUP
38 S&W 13000 CUP
38 Special 17000
38 Special +P 20000
357 Magnum 35000
357 Maximum 40000 48000 CUP
40 S&W 35000
10mm Auto 37500
41 Rem Magnum 36000 43500 CUP
44 Russian No standard set
44 S&W Special 15000
44-40 Winchester 13000
44 Rem Magnum 36000
45 Auto Rim 15000 CUP
45 ACP 21000
45 Colt 14000
454 Casull 65000
50 AE 35000



Rifle Cartridges
Cartridge SAAMI Pressure (PSI)

22 Hornet 43000 CUP
218 Bee 40000CUP
222 Remington 50000 46000 CUP
223 Remington (5,56mm NATO) 55000 52000 CUP
222 Rem. Magnum 50000 CUP
22 PPC No standard
225 Winchester 50000 CUP
22-250 Remington 65000 53000 CUP
220 Swift 54000 CUP
6mm PPC No standard
243 Winchester 60000 52000 CUP
6mm Remington 65000 52000 CUP
240 Weatherby Magnum 53500 CUP
25-20 WCF 28000 CUP
250 Savage 45000 CUP
257 Roberts 54000 45000 CUP
25-06 Remington 63000 53000 CUP
257 Weatherby 53000 CUP
260 Remington 60000
6.5x55mm Swedish 51000 46000 CUP
6.5mm Remington Magnum 53000 CUP
264 Winchester Magnum 64000 53000 CUP
270 Winchester 65000 52000 CUP
270 Weatherby Magnum 53500 CUP
7-30 Waters 45000 40000 CUP
7mm-08 Remington 61000 52000 CUP
7x57 Mauser 51000 46000 CUP
280 Remington Express 60000
284 Winchester 56000 54000 CUP
7mm Remington Magnum 61000 52000 CUP
7mm Weatherby Magnum 65000
30 M1 Carbine 40000 40000 CUP
30-30 Winchester 42000 38000 CUP
300 Savage 47000 46000 CUP
307 Winchester 52000 CUP
308 Winchester 62000 52000 CUP
30-40 Krag 40000 CUP
30-06 Springfield 60000 50000 CUP
300 H&H Magnum 54000 CUP
308 Norma Magnum 55100 PSI (Norma)
300 Winchester Magnum 64000 54000 CUP
300 Weatherby Magnum 65000
32-20 Winchester 16000 CUP
7,62x39mm 45000 50000 CUP
303 British 49000 45000 CUP (Speer)
32 Winchester Special 42000 38000 CUP
8mm Mauser 35000 37000 CUP
8mm-06 50000 CUP (Speer)
8mm Remington Magnum 65000 54000 CUP
338-06 53000 CUP
338 Winchester Magnum 64000 54000 CUP
340 Weatherby Magnum 53500 CUP
35 Remington 33500 35000 CUP
350 Remington Magnum 53000 CUP
356 Winchester 52000 CUP
358 Winchester 52000 CUP
35 Whelen 52000 CUP
358 Norma Magnum No standard
9,3x62mm No standard
9,3x74R No standard
375 Winchester 52000 CUP
375 H&H Magnum 62000
38-40 Winchester 14000 CUP
416 Remington Magnum 65000 54000 CUP
44-40 Winchester 13000 CUP
444 Marlin 42000 44000 CUP
45-70 Government 28000 28000 CUP
458 Winchester Magnum 53000 CUP

copyright (c) Paul Stephens 1999, 2000, 2001, 2002, 2003
As you can see some of the PSI pressures are higher and some are lower than the CUP readings - there really is no way to compare the two without actual readings.

PaulS

[Gordon]

Wow! PAULS! That is QUITE the table. Some of my data fits with the rifle data but glarig examples like .35 Rem and pistol abberations are really enlightening. You did a great job!:D

[ChristopherG]

Good explanation, JimW--thanks.

Hey, k say, this has gotten a little esoteric; did you get the answer to the initial question you were looking for?

[mete]

The +p & +p+ , usually refers to hangun loads and they also mean more wear and tear on the gun. You should really do some serious thinking about the extra performance being worth the extra wear and extra recoil considering that the bullet placement is the most important thing.

[k say]

yea thanks , may hav to giv reload ing a try:)

[Standing Wolf]

Jim Watson:

Thanks, eh? I knew there had to be an explanation; as feared, however, it's a little beyond the powers of my comprehension: I barely made it through high school physics a long, long time ago. I'll just stick with reloading manuals and stay a little under maximums listed. I had no idea there could be so many ways to measure pressure.

[C.R.Sam]

And...

+P an indicator of stress on the gun but not a direct indicator of bullet performance.

+P means PEAK pressure is up to 10 percent higher than normal for that particular cartridge.

Sometimes a powder switch will give (using same bullet) higher velocity AND lower pressure.

Sam

[HankB]

I remember a thread concerning 9mm standard, +P, and +P+ loads.
IIRC standard 9mm loads were not to exceed 35,000 PSI, and +P loads were not to exceed 38,500 PSI. There was no standard for +P+ loads, but several boxes I have from major manufacturers were labeled that they were loaded up to 40,000 CUP.

Note that, as already stated, PSI and CUP are not interchangeable, and there is, to my knowledge, no reliable conversion formula. Generally speaking, it looks like PSI numbers tend to be higher than CUP numbers, so it wouldn't surprise me if the 40,000 CUP +P+ 9mm ammo is above an actual 40,000 PSI.

Pressure "standards" lead to some strange anomalies . . . take the .30/06. PaulS's table shows 60000 PSI is the max, but the.270 is 65000??? Maybe its set that way because the .30/06 is more often found in rifles less robust than a modern bolt action, but in identical rifles, there's no good reason for the difference.

Also, the Europeans uses different standards of measurement - C.I.P. is the abbreviation, IIRC - which don't correspond exactly to either CUP or SAAMI PSI measurements.

[C.R.Sam]

Pressure "standards" lead to some strange anomalies . . . take the .30/06. PaulS's table shows 60000 PSI is the max, but the.270 is 65000???.



A given pressure expressed in PSI (Pounds Square Inch) will exert greater total force on the action from a large cartridge than from a smaller cartridge.

Pressure stays the same, area is increased; ergo more force.

Sam

[HankB]

A given pressure expressed in PSI (Pounds Square Inch) will exert greater total force on the action from a large cartridge than from a smaller cartridge. Pressure stays the same, area is increased; ergo more force.
Sam, that's generally true . . . to a point. But take a look at the two cartridges in question. The .270 is essentially derived from a .30/06. The case head diameter - and hence the body diameter - on a .270 is identical to a .30/06. Bolt thrust will be identical for equal pressures. (Pressure X area) Hoop stress - that is, the stress applied to the portion of the chamber surrounding the cartridge - will also be the same. So again, assuming identical rifles, and good modern brass, there is NO good reason for a difference in .30/06 and .270 pressures unless its because the '06 is more likely to be found in weaker/older firearms.

Also, note that large magnum cases are loaded to higher pressures . . . so you have larger cartridges - more area - at higher pressures than the '06. A .416 Rem at 65000 PSI puts more stress on a rifle than a .270 (or a .30/06) at 65000 PSI. And yet many rifles are chambered for both cartridges.

[C.R.Sam]

Hank right: Me wrong.

I was thinkin the 270 case was smaller at the beginning of the shoulder.
Wrong..head, length and taper the same tween 06 and 270.

Sam

[labgrade]

& to segue a bit further ...

Increased pressure doesn't mean extra velocity (in case that wasn't evident from Sam's earlier post), *& sometimes quite the opposite.

Too, using TC's Contender as an example, a larger diameter cartridge case head distributes the presures over a larger area allowing higher pressures.

JDJones used this phenom in the "old style" Contender to his advantage by using .444 Marlin cases fire-formed to smaller caliber diameters & more potent hand gun rounds - the JDJ line of goodies.

The Contender couldn't take pressures from a .308 Win, but did a right handy job with the (formed .444 Marlin) to a .309 JDJ which pushed the 165 grains to honest 2400 fps. Same thing coming out the barrel, but by distributing the pressure (bolt thrust) over a greater area, made out A-OK.

Don't ask me about why the .223 Rem was OK .... ;)

[C.R.Sam]

PEAK pressure very important in relation to strength of gun.

Bullet performance determined, mostly, by the area under the pressure-time curve.

Sam