pressure signs

[legend]

would someone please explain "pressure signs" ?

i believe they are different things to different people...


example; i loaded my grampas .305 pigmy with 26 grains of STUMPBLOWER #6,and the thing shot my old 143 grain zink wadcutters into .035 of an inch at 100 yards all day long,no pressure signs...


what SHOULD we look for,i think most people i know think the shape the primer is in is all they care about.

and it will help some people to define WHAT they should look for.

thank you.

[thx997303]

Flattened primers are a good one.

[405]

Nothing exact about pressure signs nor in reading them. But, really high pressure will show something. The problem about a flattened primer is that they can become flat in a couple of ways. 1) High pressure. 2) Too much headspace but with low to normal pressure.

Additionally. Really high pressure can force the pimer surface into the firing pin hole leaving a crater like appearance on the primer. But, oversized firing pin holes can leave the same crater effect even with normal pressure. Really high pressure can force the case base surface into the ejector slot or hole on a bolt face which leaves a shiny scrape mark on the case base when rotated out of battery (in bolt guns). Really high pressure can overcome brass memory and rebound after firing- making case extraction difficult. Similarly, really high pressure that swells brass at the case head and overcomes the brass' rebound or spring back can be measured. The comparison index for such measurement is usually something like this: Measure the case head diameter just forward of the rim or extractor groove on a fired, factory round. That is the index. That index can then be compared against other fired rounds where the pressures are unknown.

[leftiye]

Just before extraction becomes an issue, you will see bright stretch marks or scratches where the brass rubbed the chamber during expansion. It happens on straight walled pistol cases too (before sticking happens). 405 is correct about using a fired case measurement as a guide. There will be a level of pressure where if the cases expand any more it will signal excessive pressures. The factory case may even be a little hot, but pressures that will cause any measureable increase from that measurement will definitely be too hot (the chamber is then stretching). "scratching" will increase on the factory or sample fired case between the time that equal pressures and further expansion occur too.

[c3d4b2]

This may help.

http://njhighpower.com/

Look under reloading stuph

[snake river marksman]

Some writer awhile back hooked up a strain gauge to several firearms and started loading up rounds and measuring pressure while noting all of the "normal" signs of pressure. Flattened primers, cratered primers stretched cases etc. What really left a mark on me from that article was that as often as not he reached SAAMI pressure before the traditional signs showed up.

If you see ANY of the traditional pressure signs. Back off! A bunch!

[sagacious]

Flat primers alone are not a sign of excessive pressure, and can be caused by several common factors.

For example, a very low-pressure load will often smash a primer FLAT-- flatter than many folks have ever seen. Inspection of that piece of brass will lead a newbie to believe it was waaaay overloaded.

You might consider going straight to the source and read your reloading book's section on this subject. Lots of info there.

edit: The Speer manuals have an extensive section on the correct interpretation of excessive pressure signs. The manual walks you right through it, and it's far better than collecting subjective opinions on the matter. If you don't have the Speer book, buy one new or used asap. Every responsible reloader should have this info available as a reference on his reloading bench.

Best of luck. :drinks:

[HeavyMetal]

I to use the expanded case info from new factory cases measured before and after firing in the specific firearm being loaded for!

Case in point about "reading" primers: I have a Taurus PT 99. This is the M-9 with adjustable sights and a 1911 style safety which I much prefer to the drop hammer BS on the M-9.

First time I fired it I would have sworn every round was an over load if I passed such judgement based on the condition of the primer! Primer was cratered and badly bulged back into the fireing pin hole. Looked terrible!

Turns out Taurus had a run of slides that had the firing pin hole "PUNCHED" into it rather than drilled or otherwise cut.

Because it was punched in, and had very little support in this area, the slides are all a little concave right around the firing pin hole which causes this "extruded" primer condition.

Gotten to the point I can seperate Taurus and Glock case's by the condition of the primer!

So primer condition is the least of the signals I go by.

Case condition, boolit weight, powder and powder charge weight, condition of the scale used to set the powder measure. These things are all more important than what the primer looks like after firing!

If one stays within the charge levels given by the powder manufactuer's and use's case measurements taken off new brass fired in the gun he wish's to load for and use's that same brass to work up his loads the average shooter will never get in trouble unless the powder in and of itself is wrong!

Ken Waters used this very system and I have found his load information to be very accurate.

[MT Gianni]

For me it begins with a change of the firing pin print. Any elongation, deeper or wider than normal printing it gets looked at and measured if I am developing a load. Recoil or noise make me look if shooting a load at temps that are normal. Hot weather loads not shot before in hot weather get looked over too.

[mpmarty]

I don't worry about "reading" pressure signs unless I experience difficult extraction. Except for my 30 Carbine Ruger single action.

[Buckshot]

............Reading the traditional pressure signs are subjective and open to interpretation. In a revolver shooting something like 357 mag, difficult case extraction could mean high pressure, or it could mean slight machining imperfections in the chambers that the expanded case can grab. Primer appearance means nothing unless you're familiar with that primer in a particular firearm.

With some firearms like grandma's old nightstand revolver in 32 or 38 S&W you'd probably have it blown up before ever seeing what would be considered elevated pressure in a modern 38 Special.

..............Buckshot

[legend]

all thoughtfull and great information,some things i might not have thought of...


thank you all,i believe other people can use this as well.

thank you.

[MtGun44]

I tend to think that most of the time if you have any "pressure signs" that aren't just
a firearm peculiarity - like Buckshot's excellent point about rough machining in a revolver
cyl - you are probably way over safe.

There was a really excellent article on this some years ago. The author, perhaps John
Wooters, had carefully loaded rounds the were some standard pressure difference apart
and tested them to verify what ACTUAL MEASURED pressure they put out. He ran from
several steps (let's say they were 10,000 psi steps - I don't remember exactly, but it makes
little difference) below normal to 2-3 steps above safe. He showed excellent closeup pix
of the heads and the sides of the bases of the cases. Remember, several were at around
75,000 psi - way over what you should be using. The key point was that they all looked
JUST FINE - not one hint of a problem.

So - if you are seeing pressure signs in a bolt action rifle, you are probably WAY over a safe
load, like maybe 80-90,000 psi !

The good news is that most guns are really strong and they manage to put up with some
serious overpressure without hurting us. I have personally witnessed three rifles blown up
by handloads that were done improperly. In each case it was severely overlength brass in
a .223 - basically the case was crimped into the bullet by the end of the chamber and the
bullet couldn't leave. In all three cases, no injury to the shooter.

One of your best bets would be to observe carefully what factory ammo brass, primers, etc
looks like in your gun. If you see signs of pressure deforming the SAME BRAND and SIZE
of primer more or the brass looks a lot worse, you can take the factory rounds as reference.

[ScottJ]

I've been reloading since the Fall of 1992 and was taught by guys who had been doing it much longer than that.

I was taught to look at primers AND other signs such as extraction. Or bolt lift on a rifle or even changes in ejection patterns for a semi-auto.

When possible I like to have a factory reference from the gun I'm developing for in a similar loading.

For example I was looking to come close to Fed Match and fired factory samples first to see what the cases look like and how extraction felt.

Another sign not mentioned yet is stamping of the case head with features from the breech face. For example I have some .308 cases that I loaded to the point of hard bolt lift and the case head has a shiny, slightly raised spot where the ejector passes through the bolt face of my 700 (yeah, I did some less than wise things in my youth). Stamping the case head worse than a factory round is a sure sign to back down.

So, what I do when I start loading for a new gun is to shoot some factory stuff through as a baseline and then work up what I want comparing fired cases to the factory reference.

[spqrzilla]

The point is that primer signs and case head marked with ejector slots is not a sign of excessive pressure. They are signs of completely over-the-top trouble pressure.

Once I realized that primer condition was unreliable, what I've done since is stay inside of data published by reliable sources and watched velocities with a chronograph.

[c3d4b2]

Once I realized that primer condition was unreliable, what I've done since is stay inside of data published by reliable sources and watched velocities with a chronograph.

I do not wish to sound unknowledgeable, however could you kindly elaborate about what you are looking for when watching velocities?

[HeavyMetal]

He's most likely watching for velocity "spikes".

If you load a 357 158 grain boolit on top of 14 grains of WW 296 and fire it in a 6 inch barreled 357 pistol velocity should be in the range of 1275 to 1400 FPS.

If you use this load and it generates 1800 FPS something is wrong!

You might have a Super Smooth barrel or you might have misread the powder scale or you may have seated the boolit to deep or your case walls might be to thick or you may have found to only container of "Fast" WW296 on the planet!

What ever the reason one round fired over a chrony, thats been verified accurate, should cause you to cease and desist until the problem can be figured out!

Again a few loose ends with this system, as there are in all such educated guessing games, but it is a viable means to track higher than normal velocity and at least consider why such velocities are coming from a load that should not be generating them!

Being safe and not a statistic is what load safety is all about. Some type of relaible pressure reading system is going to have to be used if you intend to push the envelope with hot loads.

The two easest systems for the average shooter is case expansion or the chrony method.

Both require a batch of factory loads for "calibration" and, as long as you stay within the paramaters set up by the factory loads in the specific gun your loading for, you will be safe!

I think this is a neat thread! I hope info continues to come in we may even see some new ideas on reading case diamensions or other clever ideas!