Excessive pressure - Indicators

[Lilswede1]

Is it possible to determine excessive pressure from inspection of a spent casing?
What do you look for?
Hornaady and Lyman reloading manuals are helpful but would like to hear from a layperson.

[jdscholer]

Extremely flattened primers with metal that has cratered into the firing pin hole, is probably the most obvious one. jd

[wogpotter]

There are several signs that the pressure is already too high.
As mentioned flattened primers.
Primers that are loose in the pocket.
Smudge, or somke marks around the boltface.
Expansion of the case web, just in front of the solid head.

Here's where it gets tricky.
It's a change form normal that you're looking for, so you'll need a "normal" reference to compare to.

All primers flatten to some degreee under safe pressures, & this differs from primer make & model. Not all primers have the same amount of rounding to begin with either.
You'll need to know what a "normal" primer of your brand & type looks like under safe pressures, & compare the change to have this indication be meaningful.

The same with loose primers. The change here is caused by the case itself expanding & stretching the hole. There is normally some expansion. Is the one you are checking looser than normal? Primers are set by feel so you'll need to know what a normal feels like to see if there is a change in feel. If the primer falls out of the pocket then the load is way, way too hot.

Smoke or smudges on the boltface are another step down the road to catastrophic failure. This is beyond flattened, loose primers the hot gas has actually blasted past the primer/case junction & marked the boltface.

Case web expansion is not a visual thing, the change is too small to be seen with the naked eye. All cases expand during firing, & then contract back to close to the size before firing. How much is too much will need to be measured with a micrometer (not a caliper) . Expansions of microns beyond normal are bad signs.

All of this is subject to normal variations & a fair bit of judgment on the part of the user.

The best information I ever got was to check several cases against several suspect cases. Do several inspections of several areas. All measuring to be done at several points.
If after this there is ANY abnormal deviation you can't explain then fail-safe & take action against unsafe pressures.

[Unclenick]

The comparison to normal is a good practice. I will add case head expansion, which is what loosens primer pockets. Unfortunately, brass is an inconsistent indicator of pressure. Pressure needed to get a particular expansion in the case head or the pressure ring can vary 40% within a given gun and brass lot. So, sometimes it happens when you are safe and sometimes it doesn't when you are above what is good for the gun. You end up watching for everything and getting ready to back off when any one of them appears.

If you are loading for a bolt-action rifle, the bolt can get hard to open when the pressure gets too high. If you have a chronograph, watch out for a load that gains no velocity even though you've increased the powder charge. That or one that becomes erratic in muzzle velocity. All are signs of the chamber stretching.

[wogpotter]

Good point.
I should have mentioned that sometimes the combination of indicators can support/discount pressire warnings.

[Lilswede1]

Got back from shooting today and put spend casings under magnification.
Cannot see any of the signs mentioned by you learned gentlemen so think I am OK.
Used a small chainsaw file to test primers. Could not knock them out or loose by hand pressure - had to use small dead-blow hammer.
No smudgle or powder marks on bolt face - no measureable difference in casing size or appearance. Removed several primers and compared them to spent primers from once shot casing I recently purchased. Can't see any difference under mag glass.
I was using V-maz 50 gr. bullets this time and other than I need to adjust my OAL they shot 1/2" groups @ 100 yds.
Will keep trying - always want to do better.
FASTER BULLETS -- WILDER WOMEN -- MORE MONEY.

[jamaica]

Signs of excessive pressure:

Heavy kick!
The bolt may be stuck. (in a bolt action)
The primer is flattened.
Some metal may be extruded back into the firing pin hole.
The primer may be loose.
Some brass may have been extruded into the ejector slot.
The case head may be expanded. You need a mike to check this and even as little as 0.0005 expansion indicates overpressure.
The bolt and base of the casing is blackend indicating gas has leaked out around the primer.

[wogpotter]

"Some metal may be extruded back into the firing pin hole. "
That can be a sign as well.
Once again it's the differencebetween a "normal" load & what you are getting with an overpressure load.
Other things can cause this as well, such as a poorly fitting firing pin/boltface.

[Unclenick]

I agree with Wogpotter's emphasis on "normal". That is, normal brass appearance and measurements for your gun. The reason that matters is, for example, you could have a slightly oversize firing pin tunnel or an undersized or improperly shaped firing pin nose and any of those could give you primer cratering even at safe pressures. If that is normal for your gun, it doesn't count as a pressure sign in your gun. Same for any other case appearance or dimension that may be altered by your gun's individual dimensions.

Jamaica's point about case head expansion is also correct. Unlike pressure ring expansion, you really need a micrometer with a ten thousandths resolution to measure it. A caliper, even a digital one with half thousandths in the display, cannot measure this accurately enough to do you any good. You can usually pick up a standard thimble OD micrometer with a ten thousandths vernier for about $15 at Enco. A blade micrometer to measure inside the extractor groove is even better, but will cost much more.

One more sign of excess pressure for rifles is loss of accuracy. Many guns show greatest accuracy right up close to their individual pressure limits, but few remain accurate once excessive pressure starts stretching their receivers and/or chambers too much. In a loose gun with poor inherent accuracy, the pressure level at which accuracy begins to deteriorate is very difficult to detect. But you already know you have at least 1/2 moa capability, and that is good enough to see excess pressure start to open groups up. Loading a rifle beyond the point at which it is accurate seems to me anathema to the value of the weapon, so there is no practical reason to try to get the load hotter than that anyway.

If you can find a high accuracy sweet spot that is still within recommended SAAMI pressure limits or load manual limits, so much the better. Those numbers, except for some older load manuals, are usually on the conservative side. An accurate load that falls within them is incapable of fatiguing a modern action significantly. You will be able to shoot out many barrels in an action that is loaded conservatively, then pass the piece along to the next generation.

[wncchester]

Common over pressure signs are important but can be misleading.

Unfortrunately, "flattened" primers can be about as poor an indicator as we have. I mean, really high pressure will tend to square up the corners of a primer but it more often simply indicates excess headspace. I can make you some really flat primers with most any load even tho the actual pressure is at normal limits.

A cratered primer can occur with a normal load if the pin is too small for the hole or if the pin's spring is too weak.

Pierced primers are most often the result of a firing pin that is too long or too sharp or you have a really thin/soft primer cup.

Sticky bolt lift is valid but only indicates the pressure is FAR above normal.

Few of us know how to properly measure case head expansion well enough to gage excess pressure that way.

THEREFORE, it becomes necessary to set our FL sizer correctly for out chamber or we will have misleading flat primers. We need to know how the pin should fit and protrude from it's hole.

THEN, if we take ALL of the "normal" overpressure signs in context, we can actually get some idea of the relitive pressure of our handloads. Yes, it really can be done but likely not by a noob, so keep loads within the book guide lines.

[GAR700]

How about a primer that backs out? I have had primers that, after firing, appear as if they were left high during the loading process but they weren't. They seem to do this less as the pressure increases. Is this a sign of LOW pressure? I am new to this so please forgive if this is a stupid question.

These same rounds appeared to have cratered primers when fired from another rifle. All loads were in the middle ground of the load data.

Thanks,
GAR

[temmi]

Smudge, or somke marks around the boltface.


OR

Smudge, or somke marks around the primer pocket


Sticky / hard bolt lift...

When these things happen you are already OVER pressure

[F. Guffey]

a weak firing pin will cause 'pierced primers', gas cutting of the bolt is caused by primers backing out first then re-seating as the head or the case moves back and re seats it, it starts as smudge, then a ring, then gas cutting. a case that is not sealing the chamber will cause smudge,

It is too bad a crush/pressure (CUP) system can not be replaced with a system that would allow pressure to be measured with something in the chamber, yes, replaced with something that would be in the chamber when the trigger is pulled.

Then there are those that were using 'glide and slide', they were lubing the case to prevent it from grabbing the chamber, this could cause imprints of the bolt face to be imprinted on the head of the case, then there is the 'push feed' bolt, imprinting the extractor on the head of the case can be read as high pressure.

F. Guffey

F. Guffey

[wncchester]

"How about a primer that backs out? I have had primers that, after firing, appear as if they were left high during the loading process but they weren't. They seem to do this less as the pressure increases. Is this a sign of LOW pressure? I am new to this so please forgive if this is a stupid question."

Not stupid at all. A primer can only back out IF there is excess headspace, slop, in the chamber to cartridge fit. It's a sure sign of a very low pressure reload.

The firing pin's fall will drive a cartridge forward until it stops at shoulder, rim or belt. The primer explodes and backs itself out until it stops at the bolt face. Normally, the case will stretch back under pressure and reseat the primer to exacly flush. But, sometimes the primer won't slide freely so the case may push the primer flat as a pancake as it moves back. That may seem to be a sign of high pressure when it's actually normal pressure but caused by too much slop in the chamber.

The proper action to prevent such primer back out is to size the case properly to fit the chamber to start with. Adjusting a FL die as the instructions normally say insures the sized case will fit any SAMMI chamber but it's often much more than an individual rifle needs. Proper sizing is easy.

Try this; size a case as you normally do, prime and fire it, then set it aside.

Set your die to touch the shell holder "normally" and then back it out a quarter turn or less. Size a case and chamber it, empty. If it's too snug, and it should be, return it to the press, screw the die down a little bit more, but not more than 1/16 of a turn, and try again. Keep this up until the case fits with just a hint of bolt resistance and lock the die ring in place right there to save the adjustment.

Then, prime and fire a case sized my way. Compare the first and second case's primer protrusion. Likely see an obvious difference in the set back.

Sized properly, your cases will have no significant primer "back outs" nor will they stretch much at each firing. I frequently get 15-20 hot reloads with common cases. I load them until the neck splits, which is harmless.

[olddrum1]

Metal in left forearm. Back half of bolt lands back in the truck. Brass inbedded in forehead. One finger on right hand torn half off.

Working up a load without your glasses, Priceless.

[wogpotter]

"a weak firing pin will cause 'pierced primers"

Can you explain that differently?
I have no idea what a "weak firing pin" could be.

[F. Guffey]

Wogpotter, yes I can, a firing pin without a spring is said to 'float' the M1 firing pin 'floats' when the bolt is shook back and forth, the sound of the firing pin trying to catch up can be heard, in the case of the Ml, the spring that holds the firing pin from being pushed back by the pressure in the primer is in the trigger assembly, on a Mauser etc., the firing pin is held forward by the spring, the spring prevents the pressure from pushing the firing pin back, the firing pin is an assembly, without enough pressure from the spring, the firing pin because of the pressure X area to the square inch thing, the ability of the pressure inside the primer can exceed the ability of the assemble to maintain the dent, so as you asked, a weak spring can not hold the firing pin forward.

Thanks for the oppertunity, a weak spring will allow.

F. Guffey

[mrawesome22]

I worked a load up in a bolt action with neck sized brass. As I worked up the load past max, there were absolutely no signs of over pressure. My first shot with a load 2gr past book max made the bolt VERY hard to lift. Other than that, everything else looked perfectly fine. This was just an experiment and I don't recommend going over listed max loads.

EDIT: I've found that flattened primers usually indicate excessive headspace more than over pressure.

[Unclenick]

All primers try to back out on firing. The priming mix explodes quite rapidly, and the gas can't get out through the flash hole fast enough to relieve the pressure before it unseats the primer, which it does with some force. Indeed, John C. Garand's first military rifle design actually used primer backout to drive its semi-automatic operating mechanism. When the military went to crimped primers in the 1920's, that backup force was no longer available to him, and he had to invent his gas operating system that ultimately went into the M1 ball version of the Garand rifle. M1 ball was obsoleted in favor of M2 ball for practice and M2 AP for combat. But the rifle did not need to be altered to work with them, so the name M1 Garand remained. M72 Match ammo was the closest thing to M1 ball that was still in use beyond WW II.

The normal seating depth for a primer is about 0.004" below flush with the case head face. A little deeper is possible with depth uniformed primer pockets. As far as I know, among reloading gear only the Forster/Bonanza priming system enforces that depth. It is on both their bench priming tool and on their Co-ax press. In any event, if you have that 0.004" in an uncrimped case in a dead tight chamber (neck-sized only) the primer will still back up at least that much. As much as the headspace of the chamber is bigger than the cartridge headspace, you can add that amount to how much the primer backs out. As described earlier, it will then re-seat when the case head moves back against the breech face.

In a high power rifle cartridge, the case web sticks to the wall of the chamber, and the head moves back without the rest of the case by stretching the brass at the pressure ring (where the thick brass of the head joins the web). There is a low load pressure range in which the pressure is still great enough to stick the case web to the chamber wall, but not be great enough to stretch the pressure ring. Thus the case head doesn't back up to the breech face. That's why the primer is still sticking out when you extract it. At still lower pressures the case web does not stick to the chamber wall and the whole case backs up like a piston. In that situation the primer goes back to being reseated.

If you have excess headspace, the primer can back out far enough that the sides of the cup have so little support from the sides of the primer pocket that the pressure will actually swell the primer laterally. When the case head is forced back against the breech face it then flattens the expanded portion of the primer, giving it the appearance that the primer has gotten bigger. When you decap the case, the back of the primer is wider than the open end where it filled in the radius of the primer pocket. This is called mushrooming. It is a sure sign of excess headspace.

[wogpotter]

F. Guffey.
Thanks. I understand what you were saying now.
It sounded like actual sub standard construction at first.

[darkgael]

The whole "what are the signs of excessive in a cartridge" business borders on black magic. Don't get me wrong, I agree with virtually all that has been written so far in this thread but the fact that there are exceptions to almost all of the signs of "too much" leads me to the black magic comment.
Without some way to know what is happening inside the case when ignition occurs, looking at the outside afterwards is guesswork at best.
One note that I'm a tad surprised has not been made is that sometimes a load can be overpressure and there will be NO visible indicators. This is especially true of straight-walled cases but bottlenecked cases are also suspect.
Stay with the loadbooks, unless you have the bucks and the expertise to own and use a pressure barrel.
Pete

[wogpotter]

I agree with you about the "sticking with loadbooks" comments.

However.

It is not "Black Magic" to check with pressure signs if you are a responsible handloader. Exactly the opposite is true. You should check all your loads for safety, & checking for pressure signs is one of the responsibilities you accept when you handload.

Comparing normal to abnormal cases, combining multiple checks for various signs, and using experience & skill absolutely does not equate to "Black Magic".
It does equate to intelligent interpretation, based on experience.

[WESHOOT2]

The first sign is when you've exceeded the maximum load from your manuals.

But not always.

[TEDDY]

I never check mine.why?? because I dont load to max,dont want to, dont see any reason to.my 13 gr Red Dot and 170 gr lead bullet at 1680 ft will kill a deer dead.besides thats a very pleasant load.and 5 touching at 100 yrds is good enuf.or as they say "minute of deer".there are 3 in the freezer now and another month to go.