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Discussion Starter #1
In another section of this board I detailed how I worked up to a load consisting of a 158 gr lead swc hp /gc . By starting with a .38 load and increasing the load by 5% at a time I reach a what I call a +p++ loading. Each "+" indicates a 10% increase of Power Pistol until I topped out at 7 gr, about 20% less than a .357 load I am shooting this load out of a Ruger LCR 357 with a 2" barrel, using .38 spl brass and getting about 1020 fps. I am hoping that some of you experts can run this data through a ballistic software program and give me some idea of the pressure this load is generating. Thanks in advance and good shootin' to ya', dgang
 

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dgang, nobody in their right mind on this, or any other forum would touch a load over spec with a 10', or maybe even an 11' Pole.
 

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Discussion Starter #3
TMan, your telling me that a cast bullet going 1000 + fps is generating pressure more than a .357 can handle? We must be using different load data. dgang
 

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Discussion Starter #4
TMan, Here is the results from Quickload "QuickLOAD says that to get 1020 fps from a 2" revolver barrel you would be at about 26,600 psi, which is fine in your .357 magnum revolver, but would not be good for the half life of a light frame .38 Special revolver. Good practice would be to put these loads into .357 cases to prevent accidental chambering in a .38 Special. That's what the extra .357 brass length is for." The LCR 357 is rated for .357 pressures. dgang
 

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I can't fathom any justification in loading a super hot load in .38 brass when it could easily bust a .38 revolver if it should accidentally be tried. Certainly justified not when it is so easy and safe to load even hotter in .357 brass. But that's just me; I'm and old, not bold, reloader who still has all his fingers after some 45+ years of loading.
 

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There is justification:

If you are loading for a .38-44 revolver certainly loading to the original specifications is legitimate. Of course identification of the ammo as .38-44 rounds would be of extreme importance. This is not an uncommon practice with many cartridges used in stronger firearms such as the .45-70, .45 Colt, .30-40, and .44 Special. Indeed, law enforcement agencies had higher pressure .38+P+ ammo commercially loaded to 23,500 cup for their K-frame revolvers in the 1970's and 80's as shown below.

In this specific case however, it makes more sense to use .357 cases in the .357 revolvers and avoid the issue.
 

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What is +P++ exactly?
 

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"...in the future .357 brass it is. dgang"

Good man!


"If you are loading for a .38-44 revolver certainly loading to the original specifications is legitimate."

That only says it can be done, it isn't a justification for the potential hazard.
 

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Discussion Starter #11
jwp475, A +p indicates a 10% increase in powder for a given round. Some 9mm made for SMG use +p+ to indicate their increased pressure. In my load I used +p++ to show that that I loaded with a 30% increase in powder. A .38 spl. 158 gr. lead bullet is listed at 5.4 gr. of Power pistol, 6gr. equal +P, 6.5 equal +p+, and I stopped at 7 gr. and called it +p++. This has absolutely no sammi or scientific basis, just something I decided on to keep tract of my own loading. dgang
 

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I think the confusion is probably that this is your method alone. SAAMI defines +P as +10% pressure (not powder) rounded down to the nearest 500 psi. Thus .38 Special is:

17,000 psi × 1.1 = 18,700 psi rounded down to the nearest 500 psi becomes 18,500 psi.

For 9 mm Luger it is 35,000 psi × 1.1 = 38,500 psi, with no rounding needed as the result is already a multiple of 500 psi.

+P+ is not a SAAMI standard. It mostly indicates a round intended only for law enforcement and other public sector applications and the agency buying the ammo has to assume all liability for gun damage caused by it. For example, one fellow complained on another forum that the Federal +P+ 124 grain Hydrashok round gave him lower velocity than Winchester's generally available +P load with the same weight bullet. Well, Federal wants to sell that round to law enforcement, and the +P+ label helps them with that, but either they use a powder too fast for the application, or it isn't really saying what the pressure is.

That funny example aside, Father Frog has some posted info for other ammo, and he shows .38 Special +P+ is, by unwritten agreement, 30% over SAAMI standard MAP (Maximum Average Pressure) rounded down to the nearest 500 psi. So, you have:

17,000 psi × 1.3 = 22,100 psi, rounded down to nearest 500 psi = 22,000 psi.

That number is remarkably close to the CIP standard of 150 MPa (21756 psi), which they use for all .38 Special loads. No milder European standard exists. This leads me to believe what the ammunition industry calls +P+ is actually perfectly safe in any modern .38 Special. One might want to treat aluminum frames more gently as a matter of routine for practice, but when the flag goes up, even they will take a good number of +P+ loads without stretching. Especially newer ones using better aluminum alloys than the early ones did.

For uncompressed loads in the .38 Special, it is close to accurate that pressure increases as the square of the powder charge. So, to convert a standard .38 Special load to +P:

√(18,500 psi / 17,000 psi) = 1.04, so, using the same case, bullet, primer and powder, multiply your standard pressure charge weight by 1.04 to get a +P version.

For industry +P+:

√(22,000 psi / 17,000 psi) = 1.14, so, using the same case, bullet, primer and powder, multiply your standard pressure charge weight by 1.14 to get a +P+ version.

9 mm +P+ is not figured the the same way as .38 Special +P+. Instead of 30% over the standard load limit, 9 mm +P+ uses 20% over standard by industry convention. Again, +P+ is not a SAAMI compliant standard, but an industry creation that is a pseudo standard by general agreement and is unique for each cartridge that has it. I'm just including it to be sure it is clear +P+ does not have a consistent definition.

9 mm +P+ is:

35,000 psi × 1.2 = 42,000 psi, and again, no rounding is required as it lands on a multiple of 500 psi.

Using Ddang's 30% increase in powder, if his starting point were a true maximum load of 17,000 psi, he should tend land at about:

1.3² × 17,000 psi = 1.69 × 17,000 psi = 28,730 psi, if he started with a true maximum 17,000 psi load. The original starting load he discussed wasn't quite there, hence the 26,000 psi vicinity result.

28,500 psi is at the lower end of the normal .357 Magnum load range, so the recommendation to put these new loads in .357 Magnum cases is prudent.
 

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dgang,
Earlier Alliant powder information that also indicated pressure,shows a max load in a 357 with a 158 gr bullet and Power Pistol is 8.0 / 1305 / 33,800.

Since you are seating the bullet 1/8" deeper even though using a 1 gr lesser charge, I would think that you are definitely close to 30,000 and maybe over.

unclenick,
Great explanation.

John
 

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Speaking of higher velocity 38 Specials, in 1970, Remington introduced 2 new 38 special cartridges....
....... a 125 gr hollow point at a smokin' 1,320 f.p.s.(perhaps a misprint in their catalog?)
....... a 158 gr jacketed at 1,150 f.p.s.

Those cartriges were only cataloged for a few years and were discontinued by 1974. Perhaps they eventually discovered that the pressures generated were too high.........

John
 

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Discussion Starter #15
unclinick, You have pointed out some facts that I was unaware of. I was aware that as you increase powder, the velocity is increased approxomately by the same amount as the percentage of increased propellant, but the pressure increases exponentially. I roughly based that on load books that indicated a 10% increase of powder between a regular load and a +P load, and that the difference between the two had absolutely nothing to do with pressures. I have written down your formula for figuring increases in pressure when increasing powder and will remember the variants that effect them,ie; case capacity, type of primer being used, etc. Thank you for the input. dgang
 

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No problem. You'd think the powder and pressure and velocity would all be proportional, and for average pressure it actually is all proportional. But for that proportionality to be true of the pressure peak, the whole pressure curve would have to increase proportionally, but it doesn't. All the increase is at the breech end while the pressure at the muzzle end changes much less. As a result, for the overall average pressure to go up in proportion to the charge, the peak, which occurs early in bullet travel, has to go up disproportionately.

That happens because the added powder raises the pressure faster earlier in the burn, and that, in turn, increases the powder burn rate. Published burn rates are all figured at the same constant pressure, so they miss this change. With the faster burn rate, the powder is making its gas even faster and before the bullet can grow the volume behind it (expansion) as much. More gas in a smaller space. It's also the case that the higher pressure burns the powder more completely, so ballistic efficiency then goes up, too. Messy, but there it is.

Also, keep in mind the formula is approximate and not exact, so work up to the predicted load. It does come pretty close in most instances, though.
 

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Discussion Starter #17
unclenick, Thanks again for the explanations. One question if I could: do all powders, both slow and fast burning, reach their peak pressure in the chamber? Or does a slow burning powder continual to expand down the barrel reaching it's peak in the barrel allowing the bullet to continue to accelerate? Does the longer pressure curve extend beyond the chamber? Thanks in advance, dgang
 

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Most powders don't peak until the bullet starts to move. A super fast one can peak with the bullet base having moved forward only a quarter inch or so. A really slow rifle powder might need two or three inches. But, yes, the slow powders sustain pressure in the bore to a higher average than a fast powder does. A chart is below for the .357 Magnum if you are curious.

 

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Discussion Starter #19
unclenick, Thanks for the answer you provided. I think this would explain what Dick Casull and others were trying to do when they used duplex and triplex powder loads to get higher velocity from revolvers with big, heavy bullets. As I understand it, the powder load consisted of fast, medium, and slow handgun powders. The first layer being something fast like Bullseye, the second layer a medium burning powder such as Unique, and the top or third layer a slow handgun powder like 2400. It would appear they were trying to reach peak pressure quickly and maintain it for as long as possible. Don't know how much success they had with this process, but since nobody advocates doing this to attain higher velocity with reasonable pressures I would think it was one of those things that look better on paper than in practice. Thanks again for your info, dgang
 

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Yes, that approach has always seemed suspect to me. For one thing, just carrying the powder around will tend to mix it into a single blend if you aren't careful to use compressed loads. If mixes were an improvement, the factories would already sell it blended that way. I can see the old duplex concept of using a little bit of quick powder, like 3F BP, over the flash hole to help light a powder that is normally too slow for use in the chambering, or using some smokeless with BP to kill the fouling, but juggling multiple layers seems likely to get you into a contest between net burn rate and the amount of space needed for enough slow powder to sustain barrel pressure.

Note in the graph above, I carefully picked the loads to have the same peak pressure. The slow powder takes longer to peak, allowing the bullet to move further down the bore before the peak, creating enough additional volume (expansion) to prevent the heavier slow powder charge from causing overpressure. The result is you have the same peak pressure, but you have that pressure in a bigger volume for the slow powder. In order to have that same peak pressure in the bigger volume, the slow powder has made more total gas to see that pressure. That's most of why the pressure is then higher down the rest of the tube. It is spreading a bigger gas volume out over the whole barrel volume by the time the bullet gets to the muzzle. Some of that extra pressure is due to the slow powder not having burned out as completely as the fast as the quick powder does, but the powder will have burned to the end of its progressive burn by the time it reaches the peak, and the remaining powder burns digressively, with ever shrinking surface area, so it can't keep making gas nearly as quickly. So it's most just the expansion ratio beyond the bullet's position at the peak pressure that determines this better sustained pressure level.

They do improve powder all the time. I don't know if you've looked at the specs for the new Alliant magnum pistol and other special 300 series powders? The MP300 appears to bring about a big increase magnum velocities for overweight bullets from their load data, though it doesn't do as much for lighter ones where they even list it. They have a couple of examples that go around 1200 fps with 2400 going around 1600 fps with MP300. That's a big difference. Particularly since heavies don't leave a lot of powder room. I am anxious to try it out, but haven't seen any on the shelves here yet.
 
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