What are the signs of overpressure?

[scythefwd]

I know that flowing (cratered) primers and punctured primers can be indicators, but what are some others? I DO NOT intend to load max loads, but it is always good to know what to look for. I have only ever shot factory rounds, so I have never seen what an over pressure round looks like. Also, extractor imprints as well is a sign?

So here is my question. Will some of you more adventurous and experienced reloaders who have cases/primers that are exhibiting signs of over pressure post pictures and written descriptions of what you are seeing in the picture. I have a couple of good examples of a punctured primer and a flowing primer in the "why did this load all of a sudden become dangerously overpressure" thread. Just trying to consolidate. I see this becoming more of an issue as the economy gets worse... more people will look to reloading to save money and a picture guide of what to look for when you should be backing off your load might save a couple of fingers.

Example :

[picture]
Signs of over pressure seen in this pic
1. Primer flowing around firing pin.
2. Flattened primer
3. separated case head (not saying I'll see this stuff, but that is why I am asking)




Thanks

 

[NuJudge]

Danger.

My experience is that, especially in some calibers such as .223 and 7.5x55, one can be well over pressure before any of the usual pressure signs surfaces. That being said, there are things one should look for. They may indicate trouble, and they may not. I have a Walther KKJ in .22 Hornet and a 92FS that always crater primers, even with light loads. Here's one website with some information of the sort you are looking for:
http://radomski.us/njhp/

 

[JimKirk]

Unless you have the proper equipment to measure pressure, anything you do is a guess!

So all you have is the classic signs:

Flatten primers
Extractor hole marking
Caliber stamp peening(case head writing)
Hard extraction
Pierced primers
Cratered primer around firing pin hole
Velocity higher than normal
Others I have missed ...

Separated case heads are more of a sign of poor head space control and/or poor sizing die adjustment rather than Over Pressure. I'm sure OP accelerates separation, but is not the cause.

That leaves us with:
Good data... reloading manuals
Common sense....
and the above signs...

Jimmy K

 

[243winxb]

Some photos here www.photobucket.com/joe1944usa

 

[Walkalong]

Excessively flattened primers, and sticky extraction are two of the early signs. At this point you are into over pressure. Other signs like case head expansion, primer piercing etc are signs of really excessive pressures.

In a low presure round like .45 ACP, when you have very flattened primers you are way over pressure. That same primer in the high pressure .357 Mag is over pressure still, but not way over.

Unfortunately, all primers are not created equal, and some will flatten under pressures that barely dent others.

If you have a chrono and the velocities are too good to be true, they are.

Separated case heads are more of a sign of poor head space control and/or poor sizing die adjustment rather than Over Pressure. I'm sure OP accelerates separation, but is not the cause.

Yep.

Best thing is to keep to the manuals, & stop if anything looks or seems abnormal.

 

[Afy]

Stuff blowing up could be other things as well.
Oversized bullet, or a squib.. both come to mind.

 

[fourdollarbill]

In my 357 mag 2400 loads I was watching the primers and found fire pin puncture holes so I double checked and reduced the loads. The same happened and then I realized my fire pin in an 1894C was too long. This suggesting that primers are not the only sign, I think checking for difficult case extraction may be a better sign to look for if you don't have a chrony.

 

[Greg Mercurio]

If I recall, Ken Waters measured case head expansion of factory loads as a baseline to compare his loads to during development. Unless you are reloading a wildcat it's still a cheap and easy baseline to establish.

 

[ants]

Ken Waters measured case head expansion of factory loads

Actually, I think he used Pressure Ring Expansion. That's the brass body just barely ahead of the base.

Hodgdon, Bramwell, Speer and others report that many case heads expand about 0.0003" to 0.0005" per use (that's no typo, there are FOUR zeroes between the decimal and the numeral), and 0.0007" or more indicates much higher pressure than normal. But you will find that each and every different cartridge acts differently, especially when you realize that web thickness varies.

So you'll need a new micrometer to measure case head expansion. You can interpolate between the lines on your really nice 0.001" mike at home, but if you're using it to determine relative pressure you would be fooling yourself by reading measurements finer than the instrument was made to resolve.

 

[ants]

Also, I've always wondered about the intelligence of primers...

Same Large Rifle primer goes in my 25-35, 30-30, 270, 7x57, 30-06 [keep listing rifle cartridges here] and for IMR4350 stickpowder the same LR primer in my 7mm Rem Mag and the 300 Wby Mag.

So, just how in the holy heck does that primer know to flatten at 42,000psi in the 30-30 chamber, but to wait until 65,000psi in the 270? Smart little buggers, them primers.

Or are we simply putting too much attention on reading the primer?

 

[USSR]

...are we simply putting too much attention on reading the primer?

Yep, primer condition is the least reliable indicator of high pressure.

Don

 

[Grumulkin]

If you're loading for a gun with a weaker action such as an older revolver, a lever action, etc., you'd better stick slavishly to data from a manual and you'll hopefully never come close to excessive pressures. Excessive pressures for these guns may come with NO signs on the case or primer that you can detect.

It's in guns with stronger actions where you may run into pressure signs. You also can't assume pressure signs will be the same in every gun. Also, if you have been dong this for quite awhile, you can indeed tell a lot by looking at the primer. Pressure signs that haven't been mentioned:

1. In working up a load and starting low, group sizes will generally start out larger, get smaller and then start to get larger again. When they start getting larger again, it's a sign pressure is becoming excessive. In order to utilize this method of primer evaluation, you must have an accurate gun and must be an accurate shooter.

2. With some loads, the position of the group will at some point be in a fairly markedly different position on the paper with a small increase in powder charge. This change in group position can be a sign the powder charge is approaching maximum.

3. With autoloaders, you may start seeing scuff marks on the case body where there were none or few with lighter loads.

4. With autoloaders, the position of ejected brass may become very different as the powder charge is increased. In shooting one autoloader, the ejected cases usually land about 5 feet to the right but as the powder charge is increased may be ejected 20 feet to the right and even at times to the left.

By the way, case head separations are generally not a sign of excess pressure since you'll generally have a pierced or leaking primer before it occurs. Case head separations occur from:

1. Excess headspace.

2. Excessively resized brass (which essentially causes excess headspace).

3. From brass that has been loaded too much. Every time you resize a case, it causes brass flow forward and it has to come from some place. The flow is mostly just above the web of the case so any case that's been used too many times can have a head separation even if the load wasn't excessive. Of course, heavier loads will cause the brass to wear out, as it were, sooner and head separations occur earlier in bottle necked cases than in straight walled cases.

 

[243winxb]

Prvi Partizan .308 brass has shown high pressure with enlarged primer pockets when using starting loads. So you never know when you might run into trouble. Start low on the powder charge and work up, always applies when using new to you components.

 

[gearheadpyro]

I'm not sure what happened here, the instructor at my Basic Pistol Instructor's Course brought this in. Regardless, it's seems to fit in with the catastrophicly overpressure category. Primer was blown, as was the rest of it.

 

[Walkalong]

Primer was blown, as was the rest of it.

Yep, but the OP was looking for signs a little more subtle.

 

[gearheadpyro]

My bad

 

[45crittergitter]

Most of the common visible signs mean you're already WAY over safe pressure.

However, a velocity reading above that indicated in your reloading manual for a given load and barrel length, etc., means you have higher pressure than they did (time to stop). IMHO a chronograph is essential.

 

[Clark]

The first question is "Why do you care if there is over pressure?"
Are you worried about brass life or the gun blowing up?
This has much to do with what is the gun and what is the cartridge.

There is no book in print that tells how much each gun and each cartridge can take.

So you either follow recipes in load books or live by your wits.

I have enough trouble posting the relative accuracy advantages of truing an action, crowning a muzzle, or glass bedding an action with gunsmiths on the forum that make living from that procedure.
I have enough trouble posting about the risks of carrying handloads when gun writers who make a living off that topic are posting on that forum.
I have more than enough trouble posting about what happens when published load are exceeded without moderators and nervous nellies showing signs of over pressure.

What does it all mean?
One person's life is too short to do controlled tests on every variable, so we must pick and choose from the folklore of the gun culture.

 

[ants]

One man's folklore is another man's standards.

I got no problem with that. Each reloader has to make his own decisions and stand behind them, pulling the trigger. Let each man make his own decisions.











A man's got to know his limitations.
- Harry Callahan

 

[Sunray]

"...head space control..." No such thing. Headspace is a rifle manufacturing tolerance only. Cartridges do not have headspace.
"...flattened primers, sticky extraction and case head separations..." Also signs of excessive headspace.
Primers backing out or blown out are an indication though. Primers are a press fit, if that tells you anything. Held in by being just a wee bit smaller than the pocket. Excessive pressure will push 'em out.
"...DO NOT intend to load max loads..." Max loads are just that. Nothing to be worried about. Just don't exceed the max load given in your manual. Sometimes max or near max loads are the most accurate. My .30 Carbine load is close to max. It is the current max load with the bullet and powder I use. No fuss or bother. Don't worry about compressed loads either.
"...not sure what happened here..." Unsupported case. I'd bet on a very hot load too though.

 

[Walkalong]

"...head space control..." No such thing

I disagree. While technically you are correct, headspace is machined into the firearm, we control real live "working" headspace when sizing. If we push the shoulder back to far on a bottlenecked caliber we induce excess headspace in a firearm with that loaded cartridge regardless of whether the firearms actual machined headspace is correct.

Symantics I know, but excess headspace is dangerous, however it is created.

 

[USSR]

Headspace is a rifle manufacturing tolerance only. Cartridges do not have headspace.

Sunray,

You've been pushing this line for years, and it is no more correct now than it was then. Headspace is a relationship between case and chamber. If you lengthen your chamber, you create excessive headspace; and if you shorten your case's critical dimensions, you create excessive headspace. Don't get so hung up on semantics. Sinclair and other quality reloading outfits sell case/cartridge headspace tools. Welcome to the real world.

Don

 

[steve4102]

Primers backing out or blown out are an indication though. Primers are a press fit, if that tells you anything. Held in by being just a wee bit smaller than the pocket. Excessive pressure will push 'em out.

I disagree with the primer backing out be a sign of high pressure. When a primer backs out and stays out it is usually a sign of to low pressure.

 

[Clark]

Unread Yesterday, 10:03 PM #19 ants

One man's folklore is another man's standards.

I got no problem with that. Each reloader has to make his own decisions and stand behind them, pulling the trigger. Let each man make his own decisions.

At one end of the spectrum we have collectors that follow procedures, and at the other end we have guy living on the edge and ready to pull the trigger on an overload, but asking himself, "Do I really have a good model of the risks and which way parts might fly?'

We are all on that spectrum somewhere, but very little of our gun knowledge is independently verifiable through testing and traceable to NIST, so it is folklore.

There is a book, "How the mind works"
http://www.amazon.com/dp/0393318486/?tag=bookdigger-20
Logic is not our first choice, but we get good at logic if we think we are being cheated.

 

[ants]

Much wisdom in Clark's comments.

I just want to help rookies understand that Clark does a lot of research in this area, a scientific approach. Most rookie reloaders have no science to back them up, other than following manuals and load books faithfully.

With extensive experience, most reloaders (or at least many of them) begin to divine science from their findings. At that point, they generally stretch themselves into unexplored territory. But an unknowledgeable rookie stretching into that territory is in danger, because decisions will be arbitrary rather than scientific. For that reason, most good advice on this Forum is to stick to published data until you arrive at a point further along the spectrum of knowledge and skill.

We all strive to understand our craft better, regardless of experience and skill. Any any position on the spectrum, we must always be unafraid to ask the questions What, Why and How and accept the answers revealed to us.