38 Special pressure signs

[leathermech]

I'm asking the question now because I've never thought to ask it. "What pressure signs?"

While browsing a forum discussing working up loads for the 38 Special, talk turned to Keith's published loads, as it usually does. One feller mentioned, pressure was fine because the cases dropped from the cylinder easily. Another pal fired back how that's not the only or the most relevant (paraphrasing) pressure sign. He continued to stress that the feller was foolhardy and a missing digit waiting to happen (again, my words).

Here's what I'm thinking. The 38 Special was worked up to pressures sufficient to blow up anything but a heavy duty and cases still slipped from the cylinders. We take that same cartridge in a slightly longer case and call it the 357 Magnum, and except for nice, flattened primers, there are no signs of pressure. I've loaded 38 Special to magnum ranges (replicating Elmer's 358421 loads) with no problem in my 686. I read that to mean, essentially the same case can range pressures from 17K to 40K but in the wrong gat, the first observable sign of over pressure might very well be a top strap launched into orbit.

Before you hit your reply button, please accept that I'm not suggesting the Special and Magnum are interchangeable. No sir, not at all. What I am suggesting is an adventurous soul could easily stoke his 38 Special up to 357 Magnum pressure with no signs of danger. The feller in the post wasn't so wrong by citing his cases slipping from the wheel. Rather, he was risky by (maybe) stepping out on his published max limits because you can slip right through the Special range, skip past all the plusses and P's to land in magnum range without observing the pressure signs depicted in a loading manual. The specials are easily wolves in sheep's cylinders and I think the pal missed the lesson.

What pressure signs?? Thoughts?

 

[TucsonMTB]

What I watch for is "cratering" of the primer when the excess pressure caused it to flow around the firing pin. The tell tale raised edge around the primer hit forms the "crater".

Admittedly, I do NOT load hot revolver loads, so there will undoubtedly be other more useful replies from the guys who do.

Hope this helps, or at least sparks some more knowledgeable comments.

 

[Alk8944]

Forget looking for "Pressure signs" with .38 Special, or any low pressure cartridge! You simply are not going to see any because nothing will show, absolutely nothing, until pressure levels are 200% or more of allowable limits. Think about .357 Magnum that operates in the range of 35,000 PSIG. Rarely will you see any of the usual "Pressure signs" even at this level, and .357 is nothing more nor less than .38 Spl. in a slightly longer case at an increased pressure level.

You may see pressure signs in the Magnums, .40 S&W, 10mm, .38 Super and similar high-intensity cartridges, but even then rarely. The most common "Pressure sign" you will see in any handgun is when pieces of the gun suddenly become detached from the frame of the gun, commonly referred to as a "Kaboom", or KB.

pressure signs are strictly a phenomenon related to high-pressure rifle cartridges, those normally operating in excess of 50,000, and even then usually only once even this level has been significantly exceeded!

 

[rwsmith]

Nothing is certain here......

You can watch for primer flattening and piecing and if the cases won't eject easily, but there really aren't any really reliable signs of overpressure in .38 special and similar type cartridges short of blowing up the gun. Keep within published data. Some guns may not like max or near max loads.

 

[alwslate]

If you have a recent Speer manual read the section on pressure. There
is a good explanation of why you can't read pressures of low power
handgun cartridges by visual indicators. Some primers are softer than
others and may show cratering at normal magnum handgun pressure
levels and do not indicate excessive pressure. The advice to "work up
slowly while watching carefully for signs of excessive pressure" gets
repeated endlessly when working with cartridges that operate at
15,000 psi or so and is meaningless. Sticking to published data is the
best way to avoid trouble unless you feel like you have enough
experience to work up safe loads.

 

[ChiefStealth]

Though I have never tested the idea of over-pressure, in .38 Special, or any other pistol cartridge, I have often wondered how over-pressure would be detectable in a (relatively) low-pressure cartridge. I know what to look for. I've seen signs of over-pressure in rifle cartridges. I just can't ever remember seeing the signs in any pistol cartridge. When I work up a load, I always look for the signs. Mostly out of habit, I think. Just have never seen 'em.
One anecdote, here. At one time, I had a Colt Trooper Mk III. They were notorious for having "tight" cylinders. One day, I was shooting some light HBWC target loads. Even with that light load the spent cases were difficult to get out, sometimes. I occasionally had to tap on the eject rod to get the cases out. Some guy saw me doing that, and he moved a couple tables further over. Guess he thought that tight cases meant hot load.

 

[BB57]

As others have noted, the .357 magnum operates at 35,000 psi, in brass that has the same web as the shorter .38 Special. You're not going to see any signs of excess pressure even in 23,000 psi "+P+" loads.

Take a look at .38-44 load data as some of them ran as high as 30,000 psi - in large frame revolvers designed for that pressure. Those loads are what led to the development of the .357 magnum, and the much higher pressure is why the .357 mag was made 1/8" longer.

Like the earlier .38-44 loads, the law enforcement only "+P+" loads in the 1970s were shot in revolvers designed for the .357 Magnum and were never intended for the average .38 Special.

What you'll eventually see if you shoot those kinds of loads in a J-frame or a non Model 19 K frame will be some serious loosening of the revolver.

----

.38 Special is one of those rounds where you want to a) stick with published load data, and ideally b) use a chronograph to ensure you're getting the velocities you expect from the load. If you've got excessive velocity for the barrel length, then you've also most likely got excessive pressure and should back the load off a bit.

 

[Bruce51]

Chronograph

While over pressure signs can be misleading or non existent there is one sure way to find out.

You must chronograph your loads. The velocity reading will be the best way to find out if you're exceeding the working parameters of the cartridge.

When your .38 Special loads are clocking as fast as the known velocity of the .357 then you know that the pressure is too high.

Anything else is just guess work based on observations of fired cases.

BLM

 

[DWalt]

There is an approximate correlation between MV and peak chamber pressure, but that is affected somewhat by the propellant used, and is not very reliable. Extreme overpressure will cause expansion of the cartridge case head diameter, i.e., the area just ahead of the rim or extraction groove. But when you see an increase in diameter, you've already gone too far. I won't go into detail, but I once had a project to develop some 5.56mm loads, and I had no other way to judge excessive chamber pressure than to measure the head diameters with a digital caliper before and after firing. When it increased more than about 0.002", I stopped. Judging pressure from primer appearance is very imprecise and unreliable, except if you see primer flattening and firing pin cratering, you know it's a hot load. If the primer blows out of the pocket, you know it's really hot.

 

[Nevada Ed]

The 38 special case can go way overboard with higher fps and
still not show high pressures.

I tested full 38 loads in my "L" frame 686 357 magnum and
logged the fps . I then added more powder to three bullets.

A 158 XTP went from 832 to 979 fps. ( fast powder )
A 158 lead went from 909 to 1024 fps. ( med. fast )
A 110 XTP went from 1080 to 1305 fps. ( med powder )

These had pressure signs in the Magnum.............
I would hate to see what would happen if they ended up in even
a STEEL J frame with a mag frame, if someone let it happen.

I never load a 38 special more than a "Standard Pressure" loading
if the case does not have a +P stamp on it.

Too many standard 38's in my family ..... and any +P loads are well marked
and kept separated from the standard ammo.

Full loads are fun now and then but 98% of our shooting is with
target or standard loads, which lets us shoot more without hitting the asprin bottle.

Good shooting.

 

[BLUEDOT37]

I've loaded 38 Special to magnum ranges (replicating Elmer's 358421 loads) with no problem in my 686. I read that to mean, essentially the same case can range pressures from 17K to 40K but in the wrong gat, the first observable sign of over pressure might very well be a top strap launched into orbit.

My thought on this, like Nevada Ed mentioned, is that 38 Special cases come in various strengths. You don't want to use a "wadcutter" case for hot loads as it's far weaker. And you wouldn't want a "hot" loaded 38 Special to accidentally get in a non-magnum gun.

I have a bucket of 38 Special brass that I just don't care to load anymore for my 357 Mags choosing to use only 357 cases for light to magnum loads. Sure, you can hot load the right 38 Spcl. case but why? Just buy 357 Mag brass & have a blast, safely.

.

 

[scooter123]

Bruce Lee has the most practical suggestion. While pressure and velocity may not correspond directly finding that a load you've worked up that produces 1100 fps with a 125 grain bullet from a 4 inch revolver is a pretty darned good hint that you are way over the recommended pressure for the 38 special. In fact that's a load result pretty typical for a mid range 9mm parabellum, so it wouldn't be too difficult to conclude pressure somewhere around 27-30,000 psi.

 

[BB57]

I never load a 38 special more than a "Standard Pressure" loading
if the case does not have a +P stamp on it.

Too many standard 38's in my family ..... and any +P loads are well marked and kept separated from the standard ammo.

I take it a step farther and only load "+P" loads in nickel plated brass.

The nickel plated case makes the +P loads instantly identifiable and I never put a load with a nickel plated case in any of my standard pressure .38s.

 

[MJFlores]

As someone else already mentioned, a chronograph is a great tool to use for working up loads. I try to stick within published data, but I also use my chronograph and closely observe fired cases, as well as how the gun reacts while working up loads. Unfortunately, with plated bullets there's still a severe lack of published data so a chronograph is indispensable in cases such as these as anything else is just a complete shot in the dark. Chronographs are something that may sit around not being used most of the time, but they sure are nice to have on hand when you get the itch to experiment. Sometimes we drop $100 on a nice new set of dies and shell holder but never get around to dropping the same amount on such a useful tool.

 

[jtcarm]

While over pressure signs can be misleading or non existent there is one sure way to find out.

You must chronograph your loads. The velocity reading will be the best way to find out if you're exceeding the working parameters of the cartridge.

When your .38 Special loads are clocking as fast as the known velocity of the .357 then you know that the pressure is too high.

Anything else is just guess work based on observations of fired cases.

BLM

Measuring velocity is good, but not a tell-all. , The two don't necessarily have a linear relationship.

If you're wanting to duplicate some Keith loads, I suggest they only be used in .357s,

I've shot Skeeter Skeltons load quite a bit. It's basically a magnum in a .38 special case, but only for use in a .357.

I did flatten primers once in a .357 using a max charge of 296 (per the Speer manual of the day, which said don't reduce a ball powder load.). The report sounded like a high-power rifle.

BTW, extraction was still easy.

 

[BC38]

Measuring velocity is good, but not a tell-all. , The two don't necessarily have a linear relationship...

Can you elaborate on this? Seems to me increasing pressure would pretty much have to correlate to increasing velocity - and vice versa. How could it not?
If I can't rely on loads falling within standard velocity ranges as an assurance that my loads are withing acceptable pressure limits, what the HECK can I use as a "measuring stick" to ensure safety?

 

[Kaedan]

Is velocity always going to point to higher pressures? If so how do some companies get more velocity from a round and still claim "normal" or non +p pressures.

Something seems hokey with this.

 

[glowe]

There is a direct correlation between velocities and pressures - BUT . . . the only criteria for demonstrating this is to use the exact same loading techniques, bullet, primer, crimp, and brass, and as you increase the volume of the same powder, you will see a direct linear increase in pressure and velocity. Change any of these variables and there is no way to gauge the pressure effects by velocities alone. Random experimentation will result in having no idea of what pressures you are working with, so stick with the reloading manuals, since those loads have been pressure tested.

A great example is to think about proof testing by arms manufacturers. Shotgun companies often test with a 2X max-pressure proof load and the shotgun shell looks exactly like any low pressure target round.

I do not think there are any 100% reliable ways to visually determine over-pressure loads without physically measuring it as you shoot. Hardly anyone has the equipment or capability to do that.

 

[BB57]

Can you elaborate on this? Seems to me increasing pressure would pretty much have to correlate to increasing velocity - and vice versa. How could it not?
If I can't rely on loads falling within standard velocity ranges as an assurance that my loads are withing acceptable pressure limits, what the HECK can I use as a "measuring stick" to ensure safety?

Pressure is what creates velocity, so the relationship is very direct. However, even when average pressure and average velocity is within acceptable limits, the variation from shot to shot can become so large that some shots may be well above the maximum average pressure for a cartridge.

Assuming the loading techniques (crimp, seating depth, primers, charge weights, etc) are consistent, and the components are consistent (bullet weight, bullet diameter, case volume, etc) the pressure versus velocity curve will be fairly linear.

But even with all of the above consistencies you can encounter some areas where things start coming off the rails is in terms of excessively high standard deviations in velocity, which in turn reflect excessively high variations in pressure.

In some cases, that can be caused by a light load, where the low load density causes inconsistent ignition and pressure spikes. Your sign that you are getting into this territory is an increase in SD as the charge weights are reduced on the ladder.

For this reason, when I'm developing a light load, I'll start in the middle of the load data and work down.

The same increase in SD can begin to occur at the upper end of the scale, and it can result in some rounds having excessively high pressures, even when the average pressure is within the normal limits. Any inconsistencies in components just exacerbates this increased variability in pressure.

----

In short, you need to be looking not only at the average velocity, but also the standard deviation in velocity and understand what those numbers mean.

 

[aurora40]

There is a direct correlation between velocities and pressures - BUT . . . the only criteria for demonstrating this is to use the exact same loading techniques, bullet, primer, crimp, and brass, and as you increase the volume of the same powder, you will see a direct linear increase in pressure and velocity.

I doubt they are linear. If the pressure doubled, I doubt the velocity would double. Because the more the pressure gets the bullet moving, the sooner it is out of the barrel and the less time that pressure is acting on it. Double pressure for the same amount of time might double the speed (though friction isn't linear either), but when the distance and not the time is fixed, they won't have a linear correlation.

That said, there is a correlation, and chronographing is all most of us can do.

But say I had a book load that claimed to be 30,000 psi and resulted in 1000 fps from my gun. If I felt my robust gun was safe with 40,000 psi loads, a linear relationship would suggest I keep loading more powder until it hits 1,333 fps. However, I tend to think this would be a bad idea and that with most powders it would result in a pressure higher than my target.