My updated position paper on +P ammo (a bit long).

[1911Tuner]

Pressures

As a long-time user of 2400...Hercules and Alliant...I can personally attest to the fact that it has indeed changed. I used to use Elmer's old standby 22 grains with 245-grain hard cast semi wadcutters with nary a problem. 15.5 grains of the stuff with 150-160-grain pills in .357 revolvers was a real hoot, and produced some wicked velocities...and if I had known the true operating pressures that these rounds were burnin'...I'd probably have nightmares. But...as I said...there were no obvious problems, other than shootin' a few fabulous revolvers loose. (Hindsight and foresight, y'know)

2400 changed while I wasn't lookin'. I had put my revolvers into semi-retirement for a good 15 years, and rarely shot'em. When I did, it was with old lots of ammo loaded with the old lots of powder. Eventually, that was exhausted, so I replenished and referred back to my old data. I knew better, and even though I backed off a full 10% with the new lot and started over,
20 grains with a 240 cast bullet proved to be dangerous. New cases split,
and the ones that didn't, refused to let go of their grip on the chambers, requiring a dowel rod to get'em out. Primers flowed to fill out the pocket edges so completely that if they had been the same color, I would have barely been able to see the parting lines.

So, the data that you get for the old reliables in a 30 year-old Speer or Lyman manual no longer apply. Unique seems to be the only one from that lineup that has remained consistent over the years, and is one of my three favorite pistol powders...and even that should be approached with caution for top-end loadings.

Blue Dot is a caution. Always has been. That one has the dubious honor in my entire reloading life of being the only powder that's ever busted a revolver with a recommended load...and it was a half-grain under max at that.
It may have changed for the better since those days, but I won't be using it again for anything that has "Magnum" after the numbers.

 

[SaxonPig]

I have always used and still use the old 22G of 2400 with a 250G bullet and I have not experienced the effects you note in my 29-2. I can only speak of my own experience.

 

[1911Tuner]

2400

SaxonPig...That may mean that Alliant isn't maintaining minimum lot-to-lot variations...or they've possibly gone back to an older formulation. I noticed this in two different lots that I bought not long after Alliant aquired Hercules. Since they were both in 2X4-pound kegs, I still have quite a bit left.

How old are your lots? What lot numbers? I'd like to go back to using 21-22 grains again...but I'm a little skittish.

 

[MidnightRambler]

I too have read in a few publications over the last couple of years that old .38 special loads were hotter than today's +P loads.

 

[JohnKSa]

Interesting article in the August/September issue of Handguns.

Looks like a well researched article.

Pressures have come down some due to advances in powder technology.

Velocities have not changed, but the measuring standards have. Up until the late seventies, it was apparently common to post velocities measured in 8.375" pressure testing barrels and manufacturers often "rounded up" the numbers.

In 1977, SAAMI pushed the industry to begin measuring the velocities in 4" vented barrels which change naturally made it appear that the performance of the cartridge had been reduced.

There's lots more in the article--a good read.

'Tis worth noting that pressure is not what usually wears out guns. Pressure can blow up guns, but that's a rare and worst case scenario.

RECOIL and friction are usually what wears out guns. Shaking the gun around hard moves the parts against each other and gradually this pounding begins to loosen things up. When that happens, the added looseness allows the parts to build up more speed before they bang against each other and that accelerates the wear.

So hotter ammo will wear out a gun faster than mild loads EVEN if both loads are well within the pressure specifications of the firearm.

 

[BluesBear]

...pressure is not what usually wears out guns...

So hotter ammo will wear out a gun faster than mild loads EVEN if both loads are well within the pressure specifications of the firearm.

Testify!

I've been preaching that for years.

 

[Old Fuff]

RECOIL and friction are usually what wears out guns. Shaking the gun around hard moves the parts against each other and gradually this pounding begins to loosen things up. When that happens, the added looseness allows the parts to build up more speed before they bang against each other and that accelerates the wear.

In my experience - mostly with K-frame S&W revolvers - the problem most often seen after using (real) heavy loads is cylinder end-shake. In the case of earlier aluminum snubbies I've seen distorted cylinder windows in the frame, loose yokes, and recoil plates pushed back into the softer frame.

There is no question in my mind that heavy loads in revolvers not made to handle them accelerate wear, and may also cause gas cutting around the barrel throat in some cases. When Plus-P ammunition was introduced (and supposedly restricted to Law Enforcement agencies) this was well known and understood. Most of today's Plus-P ammunition is tamer - sometimes much so. The problem is that some brands aren't.

During those long-gone days when police departments trained, practiced and qualified using .38 revolvers and 148-grain mid-range wadcutters we didn’t see anything like the wear & tear that showed up after Plus-P ammunition was used for this purpose. This was one of the major reasons that many departments changed to .357 Magnum revolvers (primarily S&W models 19 and 66) to use their Plus-P .38 Special ammunition in.

 

[MCgunner]

Blue Dot is a caution. Always has been. That one has the dubious honor in my entire reloading life of being the only powder that's ever busted a revolver with a recommended load...and it was a half-grain under max at that.
It may have changed for the better since those days, but I won't be using it again for anything that has "Magnum" after the numbers.

I don't like Blue Dot either. I've never hurt a firearm with it, but when trying to develop loads with it, I get pressure signs long before I get the velocities I'm after. I gave up on the stuff. I have an old can, used to reload 12 gauge hot loads with it, good for that. But, i no longer reload shotgun stuff anymore.

A 158 grain load in .357 does involve less than that 15.5 grains you speak of. I ain't gonna say what I load, because it's hot, but it's less than that and I'm getting 765 ft lbs out of a 6.5" barrel (would give you a velocity, but I'd have to look it up, just remember the energy figure). That one's killed a couple of deer and it's a universal good load in all my .357 caliber guns, carbine or revolver. The bullet is cast from a Lee mold, gas check design. I love it when I can find such a useful load using a bullet I can cast, saves lots of money and gives you a sense of accomplishment. If I run out of 180 grain XTP loads, I can always fall back on the 158 grain load even though it has a little more drop out at 100 yards. It's quite accurate at that range, though.

I also very much like unique, especially in 9mm and .45 ACP hotter loads. It is also great in .38 special. 5.0 grains of unique behind a 158 grain bullet is an old standby that still works today, very accurate with a Lee TL158 grain bullet, mildly +P, but I have no qualms about shooting it in non- +P rated guns.

My other old standby for light loads is Bullseye. I have some AA#9 and I know W231 can do what bullseye does and w296 can do what 2400 does, but my loads are all around 2400, Unique, and Bullseye and I see little reason to change. I don't have to worry about keeping, but 3 handgun powders, sorta like that.

Back to the 2400 issue, I know it's likely changed, too. I haven't had such an obvious illustration of it, but I know I've backed off my old 140 grain load. I don't go so long without buying powder as you did, but I've noticed the change. I used to load that 15.5 grain load you mention behind 158s, too, and backed off the charge 20 years or so ago because I got to noticing pressure signs.

I think IMR 4350 has changed a bit, too, over the last 40 years, but that's another story. I can't find my 50s era PO Ackly reloading manual, don't know where it went. I wouldn't use any of the loads in it, but it was kind of a classic. It belonged to my Uncle and I inhereted his reloading stuff when he died since my cousin doesn't reload. Wish I could have inhereted that P08 and that JP Sauer drilling, bummer....