+P Ammo Reloads

[JettaRed]

Some load charts show a starting weight for powder and a max. Is the max equal to +P or is +P more than the max weight?

[jwrowland77]

+P simply means 10% more pressure than the SAMMI max pressure for a given cartridge.

[mboylan]

Yeah. You ate on your own for +P. Factory ammo uses blended powders and powders not commercially available. QuickLoad and a chronograph will be necessary. Bullet profile, powder burn rate, pressure curve and OAL become critical.

[steve4102]

Depends on what you are loading. There is +P load data available in a few cartridges. Check your manuals and the Free on line data.

[Nick_C_S]

To answer your question as directly as I can:

It depends on the chart. But usually, they'll specify. If not specified, assume it is not a +P loading.

But:

The term "+P" is often vague and of little real meaning, beyond marketing. I don't dispute the "10% over SAAMI spec" thing. But there's more to it than that.

To my knowledge, the term was first adapted in 1974 as an industry term to designate high pressure loadings of 38 Special, and two other chamberings - 38 Super & 257 Roberts. The industry max for 38 Special is 17K, and +P was agreed upon at 20K (which according to my calculations is about 17% more, BTW).

I haven't stuck my head in a SAAMI book in a long time (okay, ever ), so maybe the term has been applied formally to other chamberings as well (45 ACP comes to mind, possibly). Point is, when you go to your LGS and see boxes of ammo labled "+P," don't think "Oh, they must be 10% over max SAAMI spec." Think: "This company is trying to tell me that these are hot rounds." Keep it in broad terms. It's mostly marketing.

Did you have anything specific that got you thinking to ask this question? Is there any load data or something along those lines that got you asking in the first place? More info could more narrow down a more fitting answer.

[JettaRed]

Sure. My example is that Alliant Bullseye has a starting load of 3.9 gr and a max load of 4.4 gr for a 124 gr plated or jacketed bullet (not lead cast). I was just wondering if the 4.4 gr was equivalent to +P or if the 4.4 gr is simply the maximum for a normal load.

[jwrowland77]

The 4.4gr would just be the max for the people that put out that load.

You make look in 5 different manuals using a 124gr bullet and you'll probably see 5 different max charges for the same powder.

There's a lot of components that go into play. Everything from primer used, bullet used, OAL of round, firearm used and the all knowing lawyers.

[Nick_C_S]

JettaRed: It looks like you're reading from Speer #14. In which case, would not be a +P loading. "These loads do not exceed the industry maximum pressure of 35,000psi"

Not to divert the subject, but if you're loading with Bullseye, I'd be cautious of going much further than the published 4.4g. Of course, variables abound (seating depth, internal case volume, primer, etc), but Bullseye is not a propellant to go playing around with.

Bullseye is a great target propellant. Probably second to none in burn consistency with light loads. But it's not forgiving at all and is quite prone to pressure spikes - especially in a low volume case like 9mm. Bullseye can go from 35Kpsi to +P to blow-your-gun-apart in but a few 1/10ths of a grain.

If you wanna push your 124's fast, I'd seriously consider moving to a little slower powder, where the +P window is a little broader.

[Reloader2]

I thought +p cases were thicker.

[Nick_C_S]

I thought +p cases were thicker.

I think Starline's 45ACP+P cases are thicker. But no others that I know of.

Keep in mind that the function of the case is not to appreciably add to the structural integrity of the shooting system (save for the breech section). For the most part, it is to hold the bullet, propellant, & primer aligned until it goes bang.

A thicker walled case isn't going to save your gun (and fingers) if the round is over-loaded.

Keep in mind that a thicker case almost certainly means less internal volume. Less volume means more pressure (if all else is equal) - it has the net effect of increasing the powder burn rate.

[Clark]

When I started reloading 15 years ago, I read that +P was 10% more pressure made by 5% more powder.

Now I have a much more sophisticated model that includes how the user was toilet trained, to divine what the tern user meant. If he was quickly and strictly toilet trained with punishment and so is of the authoritarian perspective, it is a reference to SAAMI registered max average pressures. If he was never really toilet trained and is an anarchist artist, then the inflections are important. If he deadpans it, he got the hot load from a pre lawyer load book. If he puts a strong accent on it, it is a proof load.

[cjwils]

Maybe +P has 10% more pressure for some calibers, but others are a lot more. For example, with 45 Colt, the SAAMI pressure for standard loads is about 14,000 psi. But with commercial loads for 45 Colt +P, the pressure can be up to twice that.

[mnoirot64]

Originally Posted by Nick_C_S

JettaRed: It looks like you're reading from Speer #14. In which case, would not be a +P loading. "These loads do not exceed the industry maximum pressure of 35,000psi"



Not to divert the subject, but if you're loading with Bullseye, I'd be cautious of going much further than the published 4.4g. Of course, variables abound (seating depth, internal case volume, primer, etc), but Bullseye is not a propellant to go playing around with.



Bullseye is a great target propellant. Probably second to none in burn consistency with light loads. But it's not forgiving at all and is quite prone to pressure spikes - especially in a low volume case like 9mm. Bullseye can go from 35Kpsi to +P to blow-your-gun-apart in but a few 1/10ths of a grain.



If you wanna push your 124's fast, I'd seriously consider moving to a little slower powder, where the +P window is a little broader.

+1 on what Nick says. Bullseye is very fast and could cause some over pressure issues. There certainly are more forgiving powders out there for higher pressure recipes. Be careful!

[Slamfire]

SAAMI pressure standards are set for the whole population of firearms out there and therefore have to take into account the weaker/weakest actions. Many popular rounds, such as the 38 Special, are very old, date back to 1900 when steel technology and manufacturing controls were quite primitive. Older, lets say pre WW2 revolvers and pistols, I am unaware of any built of alloy steels and a quite a few of these plain carbon steel firearms were not even heat treated. Gunwriters make claims about the wonderful this and that of early firearms, but these guys don’t have a technical background and their claims should not be taken seriously. By the time you get to WW2 alloy steels have replaced plain carbon steels in safety critical applications because of higher yield strength, better toughness, longer fatique life and consistent properties after heat treatment.

So, in many cases you have revolvers built of modern steels and just because of the improved material, are able to handle pressures that would burst or wear out a plain carbon steel model. People want more performance, so the pressures on the older rounds can be bumped up assuming the pistol can handle it. Improved materials does not mean all post WW2 firearms can take increased pressures, far from it. Manufacturers might have made their firearm, lighter, by using less of the advanced alloys, assuming that the pressure limits in the cartridge were going to be the nice and low SAAMI specs.

Unless you actually know about the materials, heat treatment, design limits of your particularly firearm, it is best to stay within SAAMI limits. I have an 80’s Rossi revolver, modern 38 Special, made of modern materials, and it had a problem. Talking with the Warranty Shop, the guy there was emphatic about using standard pressure only loads in the thing. He had seen many of these little revolvers blown up with +P loads!

[WESHOOT2]

Please note that manuals are not gospel. Your gun may find its MAX above or below published data.
That's why EVERY manual tells you to start low and work up slow.

SAAMI +P designation in handguns is for 38 Special and 45 ACP only.

[kerreckt]

The +P designation by SAAMI is relatively new. They did not use this term until the past couple of years. My understanding is that +P started out as a marketing designation. It was ammo that was loaded to the high end of the SAAMI spec.' for that caliber. The reason for this was that ammo manufacturers had started loading ammo lighter than they had in the past for fear of litigation. This fear because of the fact that there are a lot of older handguns and lawsuits were starting to be both fashionable and expensive. Our society had become very accepting of litigating what should have been and at one time was personal responsibility. The first +P ammo was simply ammo that was loaded to the high side of the SAAMI spec. for that particular caliber. These days I don't know what +P really means nor do I care. I hand load all my ammo. My loads are suited for both the task and the firearm. Some are hot (10mm) but most are mid range or light. That's my two cents.

[Clark]

I have gone to gun shows and bought as many guns as I could carry for destructive test, carried them to my vehicle, and then gone back two more times. I now know a lot of things that contradict a lot of above posts. I will tell you that I bought a S&W 642-2 airweight revolver in 38 special in January. I shot that with +P factory ammo and owee owwee owee, you don't want any more recoil than that.

[AlaskaMike]

WESHOOT2 wrote:

SAAMI +P designation in handguns is for 38 Special and 45 ACP only.

Well, there's also 9mm +P. SAAMI MAP for 9mm is 35 kpsi, but they also show MAP for +P at 38 kpsi.

[WESHOOT2]

Thank you; I forgot completely about the 9x19 (and it also carries a SAAMI "+P+" designator, which means "no specified pressure").

[AlaskaMike]

Interestingly, in verifying the 9mm +P, I also noticed that there is not a listing for standard pressure .38 Super, although there is one for .38 Super +P.

[mboylan]

When I see things like 10% more pressure with 5% more powder, it definitely makes me believe that most reloadets should stick to the books. Pressure vs powder is not linear. It's a curve. When you are using a coffin corner powder like TiteGroup in a small 9mm case that curve spikes very high once you start going over the max.

[Slamfire]

Pressure vs powder is not linear. It's a curve.

It is a curve with an exponential slope and it turns out that humans don't "think" in exponential terms. Just a little more powder and the pressure can double, triple, quadruple, or even more.

[JD0x0]

Max SAAMI '+P' pressures.

9mm Luger +P - 38,500
38 Special +P - 18,500
38 Super Auto +P - 36,500
45 Auto + P - 23,000
257 Roberts +P - 58,000

[Clark]

mboylan

When I see things like 10% more pressure with 5% more powder, it definitely makes me believe that most reloadets should stick to the books. Pressure vs powder is not linear. It's a curve. When you are using a coffin corner powder like TiteGroup in a small 9mm case that curve spikes very high once you start going over the max.

When we look at the OP's example, we get a 24% increase in pressure from a 17% increase in powder.
But those loads are off the scale wimpy.

If we look at 5.54 gr Bullseye 124 plated making 35,000 psi and 5.79 gr Bullseye making 38,500 psi, we are looking at a 10% increase in pressure from a 4.5% increase in powder.

[Slamfire]

I now know a lot of things that contradict a lot of above posts.

Don't be mysterious, put that knowledge in the public domain.