Demystifying +P
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Old 09-21-2009, 01:15 PM   #1
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Default Demystifying +P

The inside scoop on +P
By Dan Johnson

Most shooters know the "P" in the +P designation on a cartridge headstamp stands for pressure and indicates that the cartridge is loaded to higher chamber pressures and thus higher velocities. But many are confused as to exactly how much pressure is added and how safe these high-performance loads are. I believe this confusion is contributed to by people in the industry, some by firearms companies that understandably wish to err on the side of caution in our litigious society and some by small ammunition manufacturers looking for an edge in a highly competitive market.

The +P designation came about for a very simple reason. As advancements were made in the quality and strength of both firearms and cartridge cases it was determined that some of the older rounds were capable of operating safely at higher chamber pressures in modern firearms than those originally established. Since firearms--and cases, for that matter--are durable goods that last for decades, even centuries, it was not feasible to simply increase the standard pressure specifications for these cartridges. There are too many old firearms around that could not handle the increase safely. So SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) uses the +P designation to separate the new pressure limit for these old cartridges from the old lower standard.

It is important to understand that SAAMI is the principle organization in the United States actively engaged in the development and promulgation of product standards for firearms and ammunition. Ammo specifications are not overseen by the Consumer Product Safety Commission or any other branch of government. Consumers should be aware that only manufacturers that are members of SAAMI are bound by the Institute's guidelines.

All the major American ammo manufacturers are SAAMI members, and most smaller outfits also abide by SAAMI guidelines, but I have seen ammo from one or two small manufacturers offered in calibers such as .40 S&W and .357 Magnum with the +P designation. Since SAAMI does not specify +P ratings for these cartridges there are only two possible explanations. Either the ammo is loaded to higher pressures than SAAMI deems safe or the +P designation is just marketing hype. Be aware, all comments in this article regarding the safety of using +P ammunition are related to SAAMI-sanctioned +P loads only.

Perhaps the careless use of the +P designation contributes to the caution on the part of some firearms manufacturers. Some manufacturers make vague statements in their owner's manuals regarding +P ammo that I feel adds to consumers' confusion. For example, some manufacturers of 1911s state, without explanation, that +P .45 ACP ammo is not recommended for use in short-barreled models. This is not due to any concern over chamber pressures. All modern 1911s in proper working order will safely handle +P pressures. The concern is the increased slide velocity produced by the hotter ammo, which affects the functional reliability of the handgun. These short-barreled variants of the 1911 are sometimes finicky, and a recoil spring tensioned for a particular power level of ammo helps to ensure complete reliability. Loads beyond this power level are not only more prone to jam, the added recoil causes more stress on the frame.

Another area of concern for some shooters is with the .38 Special +P loads and small-framed double-action revolvers. These little snubnose .38s have long been popular due to their light weight and concealability but are necessarily not as strong as beefier models. This is especially true of older handguns that may not have the quality of steel available today. I do not know of any current models in production that are not OK'd by the manufacturer for use with +P ammunition, and frankly, if I did I wouldn't fire the thing with any ammo. As stated earlier, SAAMI-specified +P is simply a modern standard for maximum pressure in these veteran cartridges, so if a newly manufactured handgun will not handle these pressures, I want no part of it.

I would be remiss not to discuss another P rating: +P+. This designates that the cartridge is loaded above SAAMI specs for +P ammo, and most manufacturers restrict sale of these loads to law enforcement, for good reason. These loads are carefully tailored for modern service handguns and may not be safe in all firearms. Thus they are not offered to the general public.

I feel we in the industry should make an effort to demystify +P loads. They are not, as some shooters believe, loaded to borderline pressures. The increase in pressure is moderate. For example, +P .45 ACP ammo is loaded to a maximum pressure of 23,000 psi compared to 21,000 psi for standard loads. Compared to the maximum pressure of other autoloader rounds, these pressures are very mild. The maximum pressure for the .40 S&W, for example, is 35,000 psi.

Any increase in pressure and velocity, however, does put more stress on the firearm. For this reason I use +P .38 Special ammo sparingly in my Chiefs Special, and my 1911s have heavier-than-standard recoil springs. It just makes sense to minimize stress on the firearm as much as possible. I am fond of my handguns and want them to last.

Plus-P ammunition can raise the performance bar for your handgun, but a trade-off is more recoil and muzzle blast. In some cases it is worth it, such as when a little more velocity is needed to ensure reliable bullet expansion. Velocity increase is modest, however. On average, +P ammo is about 50 to 100 fps faster than standard ammo, sometimes less. In fact, I have encountered some +P loads that were slower than some standard loads available. As always, choose ammo wisely based on your needs.

The shooter considering using +P ammunition should follow the same safety precautions advisable with any ammunition. Make sure the firearm is in excellent condition and is approved by the manufacturer for the ammunition. If it's an autoloader, make sure the recoil spring is properly tensioned for the ammunition. And make sure the ammunition is from a reliable source and loaded to SAAMI specifications.
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Old 11-30-2009, 12:14 AM   #2
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Good info thanks!

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Old 01-17-2010, 06:17 PM   #3
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Old 01-31-2010, 07:02 PM   #4
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Old 03-12-2010, 01:14 PM   #5
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Old 03-12-2010, 01:34 PM   #6
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Thanks Cane

Good stuff
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Old 03-12-2010, 10:04 PM   #7
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Great poop. The things we sometimes think are the most desireable can turn out to ruin our day.

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Old 03-20-2010, 04:55 PM   #8
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I have a quick question.Are there .40S&W+P loads?I have never heard of them or seen them,and if they are not made for whatever reason,what advantage is a .40S&W over a 9mm seeing as 9mm can be in +P and +P+ and has the same or more energy than a standard .40S&W?

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Old 03-21-2010, 03:00 AM   #9
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Default Power/ cal. differences of ammo.

Quote:
Originally Posted by ninjatoth View Post
I have a quick question.Are there .40S&W+P loads?I have never heard of them or seen them,and if they are not made for whatever reason,what advantage is a .40S&W over a 9mm seeing as 9mm can be in +P and +P+ and has the same or more energy than a standard .40S&W? I haven't refreshed my memory lately, but If true it's VERY rare indeed at least until the design of the 9MM changes a bit.
When I 1st started acquiring firearms back in the 80's I would often sit and look at a 9MM round and wonder why the ammo Co's didn't just load/design a 9 with a high enough pressure to = a full power .357 Mag out of a 6" in. S&W 586 barrel but deliver that energy out of 4" 9's (IMHO They could redesign it to do that and I would buy it, the .357 Sig is a good round and almost right there but they quit adding psi before they got it all the way there, so another dropped ball by the industry).
well it's been 20+ yrs . . so . . maybe they will one day but I'm not gonna hold my breath and wait for it any longer.
Note:
Remember as stated by Canebreak the differences of the definitions of +P ~VS~ +P+ Ammo pressures, also bear in mind all bullets make a hole of variable size but what is the most important part of getting the desired result, is where *YOU* put that/those HOLE/s!

Some .40 S&W loads such as the Corbon 135 grn reach the 500 ft lb mark which is very difficult to do with a 9MM even with a 90 grn +P+ load which might also be pretty hard on some of the available 9MM handguns, some also feel that the 135 grn JHP .40 S&W do not penetrate deep enough and if that is the case then a 80 grn 9 JHP is definitely going to be too shallow in penetration.

If you research and study commercially available defensive handgun ammo, you will find that "some" ammo offerings in various calibers (9MM, .38 special, .38 super, .40S&W, and even .45 auto) that will overlap in power level & sometimes performance.

My 165 grn +P .45 Auto HD round is pushing over 500 ft lb's closer to 600 ft lb's (still penetrates 13" of jello) so the differences between cals "can be" significant, FWIW the 9 shines with 123/127 grn Gold Dots, some people prefer to use slow and heavy
for cal ammo . . to each their own; the 9 has worked for people for many years, (IE; Wild Bill Hickock) so has the .45 and back in the days of WWI WWII the .45 Ball was considered (and I believe battle proven in the Philippines against the enemy to be more effective than .38 RN/ball or the 9MM Ball rounds) I do not advocate Ball for HD/SD it will work but if there is better made and you can get your hands on it why not use that instead of the ball for serious social work, I would use Ball for practice ammo and only use it for HD/SD if I had no premium HD/SD ammo at the time an urgent HD/SD emergency arose.

Hope this helps you get a better grasp of cal power differences.

N.D.
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Old 03-21-2010, 03:23 AM   #10
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Just a note that ALL .38 Super ammo is "+P". This designation was added in the early or mid 70's (I think) to distinguish it from standard .38 ACP rounds.

A pistol in .38 ACP will chamber and fire the much higher pressure .38 Super. Once.

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