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Discussion Starter #1
What is it. I don't know because I never buy pre packaged rounds for anything (except rimfire of course). If +P is just a larger charge of propellant, I do that all the time as I tend to load everything at the upper SAMMI limit (and sometimes way more, depending on how I jump my bottleneck rounds). Straight wall, not do much but I do tend to load them hot. Like a solid bang.
 

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+P is a SAAMI standard; while more propellant might be the cause, there could be others as well.
 

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As you know, SAAMI has set maximum pressure limits for each cartridge. Along about 1971 or so SAAMI decided to lower the max pressure for a few handgun cartridges. They were 45acp, 9mm, 38 super and 38 special. These were all calibers that had been in use a long time, and over the years there had been a lot of cheap imports and even cheap domestically made guns of questionable strength in those calibers, so lowering the standard pressure should make them safe. At the same time as when they lowered the max pressure on these particular cartridges, they also created a new class called Plus P. The Plus P maximum pressure was set at what the old max pressure had been before they lowered it.
Plus P ammunition can be made by either adding a little extra propellant or in some cases changing to a different propellant to propel the bullet fast and still stay within pressure limits. Technically there is nothing that says a Plus P round has to be faster, it just has a higher pressure threshold.
A S&W 38 Special made in 1969 was made to shoot ammo with a max pressure of 20,000 PSI, because that was the max in 1969. Remember, Plus P did not exist yet in 1969. So in 1971, SAAMi changed the max for standard 38 special to 17,000 PSI, and set the max for Plus P 38 Special at 20,000 PSI, so while there is no way a gun prior to 1971 can be marked Plus P, since it didn't exist, it can certainly handle the pressure of Plus P because that's what they were all designed for prior to 1971.
 

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Discussion Starter #5 (Edited)
Plus P is obviously the only ammunition available for purchase to first time posters on this forum.
I've read that and why I asked in the first place....:D Being an 'I build my own' person, I wasn't sure what the connotation '+P' referred to.

Probably shouldn't allude to it but I pay little attention to published SAMMI specs. When I load, I load for maximum accuracy at reasonable velocity with little regard to charge weight. Actually, the only time I refer to a charge weight spec is when I'm building a particular load and then I use a median charge to 'dial in the round and then start jumping the pill incrementally to find the accuracy node (because every chamber is different). Once I find the node, I increase the charge weight until the MV is where I want it, there is no brass wipe on the bolt face and the round ejects properly. That may entail bumping the shoulder for extra headspace as well and other aspects like neck tension and concentricity.

of course that only applies to bottleneck rounds but I have 'stretched out' my 460 handloads as well and they also seem to group better longer, than set to spec. Did the same with my 44RM with the same result btw. I run them at maximum SAMMI spec all the time.

But then I like to experiment.

Thanks for the reply to the +P thing. I really didn't know what it meant.
 
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Plus P can be a bit of a scam> As reloaders know, different powders produce different results. I can load a 9mm, 124gr round that is Plus P with one powder with a velocity of 1120fp, while getting 1150fps with a different powder and a charge that is not in the Plus P range. People automatically relate Plus P to higher velocity, but it really is all about pressure, not velocity.
 

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There are only 4 cartridges lised by SAMMI to have +P ratings.
They are: 9MM Luger, 38 Super, 38 SPL, 45 ACP. There is no SAMMI +P for .380, .357, .41 or .44 Special or Magnum, contrary to common belief.
Any cartridge listing a +P rating outside of the 4 listed as +P approved are not accepted pressures by SAMMI.
Many firearm manufacturing companies state in their literature, and warranty policies specifically state that +P ammo should not be used, and will void the factory warranty.

Some cartridges are listed as +P+, and they are providing pressures well above the pressure standards by SAMMI, and should not be used in any firearm, unless the manufacturer of the firearm indicate in writing that the firearm is capable of handling "+P+" ammo....and none do (not even the "BFR" series of pistols which are known to handle just about anything that can be made).
Some ammo companies are well known for producing ammo that is "Hot" and should not be used in anything other than modern weapons in excellent working condition.
 

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Over pressure ammunition designated +P has slightly more powder than standard velocity ammunition. Headstamps are marked +P to indicate this loading.

Commercially it is very profitable. There is a minuscule cost difference between producing standard velocity and +P ammunition, amounting to the cost of a few grains of powder and amortized testing expenses. Many use different profile bullets intended to perform differently in terminal energy dissipation. For this they charge 40% more.

The simple truth is that in order to stop an attacker, you have to hit them. Many people just learning to shoot have difficulty with recoil management and follow through. That will impact accuracy in a range situation, and even more in a tactical one. If you don't train to manage the recoil, you'll miss subsequent shots.

For that reason, I consider round count more important than using over pressure ammunition in self defense situations. That also informs my choice for 9mm rather than larger calibers for most defense carry handguns.

There is quite a bit of "image" advertising and influence involved with first time handgun buyers. Unfamiliar with firearms and ordinance, they tend to select what other people they trust tell them to pick. They are anxious that their choice will "be enough" to defend themselves. But instead of following through on that anxiety to actually invest their time and money in training and education, most think they can buy security in the objects (handgun and cartridges) and shove them in the drawer after shooting them once or twice.

This is a serious mistake. It takes time to develop familiarity with firearms and the skill to use them safely, even if they are approached with the right attitude. It also takes someone with skill in coaching to help new shooters get on the right path and grow their skill.

If security is your problem, and anxiety drove you to buying a gun you're being driven by emotions. The same emotions make you vulnerable, and thinking that buying the most powerful ammunition will protect you without the skill needed to defend yourself reflects more of the same emotional thinking.
 

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"+P" is more than the powder charge and bullet weight, it's also about the cartridge OAL (the case air space).
 

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Discussion Starter #11
"+P" is more than the powder charge and bullet weight, it's also about the cartridge OAL (the case air space).
Not sure what you refer to as 'case air space'.

All cases and loads will 'develop an air spacer' over time as the propellant settles during handling from the manufacturer to the distributor to the retailer, to you..., the end user.

I don't like the commonly used term 'powder'. It's not powder at all (in the sense of powder like talcum powder). Propellant is actually produced in an extruded sheet, much like paper and then 'chopped' for lack of a better word) into various shapes, spherical, triangular, rods and other shapes depending on the type and projected burn rate. I think Gearchecker saw my propellants on the shelf, I have many propellants in many different grades for many different applications, just like I keep many different grades of primers. The most often used propellants are always bought in large quantities (because I use a lot so the little pound containers don't work for me from a cost standpoint).

All propellants settle over time in a loaded case so every loaded case will develop an 'air space' over time, even if on the initial fill, the case is filled to maximum capacity. In fact, some loading I do are what is called a 'compressed charge'. That is where the case is filled to maximum volume and pill insertion compresses the charge. To charge a case to maximum, you must employ a drop tube of sufficient length to allow the propellant to settle in the case without overflowing the case mouth.

Neither here no there really.

Internal case pressure is a direct result of how a propellant burns (burn rate). That burn rate is what causes the pressure rise before the bullet begins to move from the case into the rifling (or forcing cone) of a handgun. Once the bullet (projectile) leaves the case mouth and enters the forcing cone / rifle lands, the pressure drops to zero, the case body contracts and the sequence of events allows you do remove the 'spent' case which is why it's imperative the case body is never annealed or the case will never contract and removal can and will be extremely difficult.

Without getting into a technical discussion, suffice to say that when 'jumping' a projectile in relation to a particular chamber / cylinder to forcing cone dimension, you can control to a great extent the MV as well as how the projectile enters the rifling and terminal accuracy. You can jump any projectile in and case or caliber (except rimfire of course) but you better know what you are doing and it takes time and patience to develop an accuracy load.

I find it interesting that I can actually 'jump' a straightwall handgun round and tighten up the groups. Sometime, when I have the time, I may experiment with adjusting the propellant charge to alter the MV as well but for now, I was surprised that jumping the projectile made a decided difference in how the groups printed down range (loading to maximum charge as it relates to a particular bullet manufacturer, in this case Hornady.

More to come on that at a later date.

In as much as I never buy factor rounds for anything, mainly because I don't know what they contain as far as propellant is concerned, or what primer is being used and that has always been a point with me, because I want to know what is inside before I ignite a cartridge, I always roll my own'. I know what is inside and I know what the cartridge will and will not do.

Besides, it's fun to build a very accurate and repeatable load but it takes lots of time and lots of components, emphasis on time.

Then there is internal ballistics and external ballistics and how factors like wind, temperature and barometric pressure impacts shot placement and propellant burn rates but maybe for another time.

Suffice to say I got some clarification on +P. had no idea what it meant.
 

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if you diminish the air space by seating a projectile deeper into the case, decreasing the cartridge OAL, that alone will create more pressure during ignition/detonation of said cartridge.
 

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To simplify it, all it is is pressure exceeding the "standardized" non +P load as indicated by SAAMI.

It is the gateway ammo to +P+ and Buffalo Bore ammo!:D

Most load data is simply the upper load of a non +P load. It is much to do about nothing.
 

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Discussion Starter #14
To simplify it, all it is is pressure exceeding the "standardized" non +P load as indicated by SAAMI.

It is the gateway ammo to +P+ and Buffalo Bore ammo!:D

Most load data is simply the upper load of a non +P load. It is much to do about nothing.
Unless of course it blows up in your face... Always a distinct possibility with an overpressure event. Handguns, not so much (except extraction of the spent case can become an issue) but long guns manufactured prior to 1990, big issue, Actions on long guns built before 1990 have no avenue for the escape of an over pressure situation except back down the bolt raceways or out the back of the action (in the case of a falling block / rolling block action) which equates to an 'in your face' event. Actions produced after 1990 are cross drilled to let 'the fire out' sideways instead of straight back which greatly lessens the in your face physical damage you will sustain from a failed case.

Candidly, I've 'let the fire out' before. Quite an unsettling experience.
 

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Discussion Starter #15
if you diminish the air space by seating a projectile deeper into the case, decreasing the cartridge OAL, that alone will create more pressure during ignition/detonation of said cartridge.
That depends entirely on the burn rate of the propellant. Slower burning propellants will lower the pressure and get the bullet moving before an overpressure event occurs but then getting the bullet moving has a lot of conditions as well. How heavy the crimp is, the tension on the case mouth and how hard the brass is all impact how the projectile releases from the case and how quickly it becomes mobile.
 
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