Pressure signs?

[danski26]

First, before I ask my question, let me give this disclaimer:

I am not loading higher than recomended pressures. I am not advocating loading higher than recomended pressures.


I have been thinking lately about max pressures and brass giving high pressure signs. Let say that you have a cartridge that has a max pressure of 50,000. In one rifle the 50,000 rounds shows no signs of "high pressure" in the brass. In a another rifle that same 50,000 round does show high pressure signs.

Now we have to assume that all variables are the same here. Barrel, chamber, brass, powder, boolit.....ect.

Is it safe to say that the rifle with no signs of high pressure with the brass has LESS of a chance of failure? Or do you think they would still be equal?

If the answer is yes, then the next question is; is a rifle that is firing that same 50,000 max recomended cartridge at 60,000 and showing no signs of high pressure in the brass also have "LESS of a chance of failure" than the one at 50,000 that is?

To put it another way....do you think that if brass showes no signs of pressure, it might be because of a stronger firearm and therefor actually there is less chance of failure?

I don't dissagree with the notion that a round may be over max pressures even if it shows no signs of pressure. I am wondering if that automaticly makes it more likely to fail when compared to another firearm actually showing those signs?

[btroj]

It may not be due to firearm strength but rather the precision with which the gun was assembled.
Good example- BR shooters use charges that are above what some load books recommend yet they don't often have pressure signs. The chambers are cut to minimum dimensions, the brass is fit to that chamber and is minimally sized, the bolt lugs bear evenly, and so on and so on.
The lack of signs is due to the precise fit of everything involved in firing. It certainly does not mean the pressure is not there.
As for chance of failure- what kind of failure? A pierced primer? Blown primer? If you mean a ruptured case they I would say that takes way beyond normal pressure. I bet a good bolt gun would take ALOT more than 50,000 psi before it let the case go. How high? Can't say but it would be an extreme overload.
I think the gist of what you are asking is this- does lack of pressure signs in a gun with a max load mean that rifle/cartridge combination is less likely to suffer a catastrophic failure? I would say who knows? Still too many variables. I will say again, this type of failure requires way beyond normal pressures. Think proof charges. The guns must hold. What pressure does it take for the gun to let go? I don't want to think about that.

[danski26]

That kinda what I'm thinking about. That benchrest rifle is made to tighter tolerances, can it handle more pressure? Sure. Does that mean any rifle that is not showing signs of too much pressure with the brass can handle it? I'm not sure......

[runfiverun]

it'll handle it but which shot is the one that it don't?
chamber roughness,oil,bolt set back,one carbon spot...

[S.R.Custom]

ASTM B129 standard specifies small arms cartridge brass to be MFR'ed to a minimum of 60-62KPSI yield strength.

In other words, if you're getting expanded case heads in a rifle, you're exceeding 60KPSI. (So yes, you can quite handily exceed 50KPSI with no signs whatsoever.)

Getting pressure signs (exceeding 62KPSI) in a modern bolt gun is a non-issue; barrel steels typically have a yield strength in the neighborhood Of 100-120KPSI.

On the other end of the spectrum, the steel in GranPappy's turn of the century Winnie 30-30 or .38 S&W was good for only 60KPSI yield strength. If you were lucky. (Given the sorry state of alloying & heat treating back then, you could not rely on anything more than the dead-nuts softness of the annealed base metal.) So if you're getting pressure signs in those old, low pressure guns, you better be in good with the Lord...

You can read all about it here. It'll cost you $40, tho:
http://www.astm.org/Standards/B129.htm

[flounderman]

no two guns are created equal. a tighter barrel or a smoother barrel will make a difference because of the resistance it offers. the design of the bolt face as regard to an ejector slot or a solid face will make a lot of difference in how much pressure an action can handle without case failure. the case is not supported over the ejection slot and the bigger the slot the bigger the unsupported area. if you blow a mauser up, the case will probably burst over the slot. if you get different pressure signs with the same load in different rifles, you probably are getting different pressures. a chronograph will show you what is happening.

[4given]

I have never had any problems with load development for MODERN bolt action rifles by watching for the usual pressure signs like flat primers & etc. I've never had anything suggest that loads that did not exibit the usual high pressure signs to have high pressures anyway......

[spqrzilla]

A big problem is that the traditional "pressure signs" are not reliable indicators.

[leftiye]

If you don't get brass flow (shiny spot over ejector hole for instance where brass was pushed into hole - 700 Rem), then you're not in danger of Kabooming. Thas if you've done your part and gotten that far - pressure signs aren't of use unless after the gun is shot it is still together. As Supermag (SRCustom) said, the gun will hang together way beyond brass flow. UNLESS escaping gasses under high pressure get to where the gun isn't designed to handle them. It is always the gasses that do the deed. But if you don't have brass flow you're probubbly safe.

So, as 4given said you won't blow up a gun before you see pressure signs. More specifically before brass flows. Pressure signs may not tell you how much pressure you're building, but the next case is likely to look the same, and if the load is reduced, the signs will abate in proportion to the reduced charge. To rely solely on a chronograph to me should (or should we say can?) only happen way after you've doped out a load, and pressure tested it, and read the signs. As was said - neither process works after there is a kaboom. Thas why we start low (ya think?)

[plainsman456]

I don't really look at primers,just at the cartridge case.
If there is a mark there they are too hot.All rifles are not the same though.
Some handle the same load differently.You need to look at them as individuals.

[Bret4207]

"To put it another way....do you think that if brass showes no signs of pressure, it might be because of a stronger firearm and therefor actually there is less chance of failure?"

IMO when you talk of "a stronger firearm" you open the ball for all sorts of interpretation. Some guns show a lot more pressure signs a lot earlier than others. It's really kind of a krap shoot saying one gun is "stronger" than another when the brass is the weak point. I'm non-committal on drawing a conclusion from traditional "pressure signs". I've seen too many flat primers from low end loads and perfect primers from allegedly hot loads. Primers alone are a poor way to judge pressure. By the time you get to brass flow ( had 2 cases of that last year!) other things are happening that should tip you off.

The one thing I'm firmly convinced of is that many people completely over look what I consider to be high pressure signs in factory ammo and others are overly cautious if it's a reload. I understand why, but it makes no sense to me.

[drklynoon]

I would be inclined to think that a springier gun should show more early warning signs of over pressure. I would think that the "stronger" gun might be more apt to give little signs until the kaboom.

[Rocky Raab]

New guns have to withstand one shot with a proof load. ONE.

Even the strongest gun expands and flexes under pressure (that's what makes strain gauge pressure systems work). Past about 65,000 psi, the fatigue of flexing multiple times can and will eventually result in failure - even if that steel originally had a 100Kpsi yield strength. Flexing weakens metals - as you'd know if you had been flying on a Southwest Airlines jet last Friday. You can indeed get away with high-pressure loads - but not forever. As mentioned above, which shot will that gun's last?

As I've written before, the time between trigger and tragedy is far too short to change your mind.

[danski26]

Thanks guys for the interesting, informative and courtious answers.

[454PB]

New guns have to withstand one shot with a proof load. ONE.

As an interesting sidebar, when Ruger was test developing the SRH in .454 Casull, the company that produced the SS for the gun fired 300 rounds of 90K PSI proof loads in one cylinder.

[Rocky Raab]

When Ruger introduced their first 9mm semi-auto, they THREADED the barrel and screwed in a bolt until it touched the tip of the chambered round - and then shot it.

The gun held. Ruger does indeed build 'em strong!

[454PB]

Yup....the P-85. I have one.