Ok, so this is probably stupid question #4375 for this week.

What would "max pressure signs" look like?

Thanks!

They are the ones that show just before you exceed max pressure.

quote:

Originally posted by Ol` Joe:
They are the ones that show just before you exceed max pressure.

That much I know. My qustion is what physical signs are they? Where do you find the signs?

In my experience the most reliable way to read a turn bolt rifle for excessive chamber pressure without a pressure test set-up is harder bolt lift and stiffer extaction. I am meaning with a rifle that extracts factory ammo easily. The handloader won't always find this phenomenon only with listed max charges either, as I have seen it with charges well below max. You can read primers for flattening like tea leaves and I won't argue that higher pressure will start flattening primers, but the bolt lift will get sticky before the primer pockets get expanded. At least this is what I have seen.

Gotcha! Thanks!

So I am looking for:
Stiff bolt
Poor discharge
Flat primers

All most sounds like a Viagra commercial!

These are not "Max pressure signs" they are
signs of over pressure. The brass is starting
to yield. Time to back off befor you are in
real trouble.

Except that primer appearance can be almost meaningless in gauging max pressures. Flattened primers can happen with very low pressure loads, and some known excessive loads will not show "classic" flattened primer appearance. Speer talks about this on pages 59-61 of their Manual #14.

A smoothly operating bolt may not mean a safe load either. My MkV in .257 Weatherby will shoot 100-grain bullets at near 3800 fps and not show stiff bolt lift with PCM brass. Clearly this is a 'way over max load, but primers and bolt lift seem fine. I do not use this load BTW, I'm happy with a 'normal' 3600 fps.

Loading manuals used to use the "classic" high pressure signs like the above to determine their maximum listed loads. But once they started using pressure measuring equipment they found that many many loads they thought were fine were well over SAAMI pressures. This is the real reason that max loads have dropped over the years - not the influence of lawyers. The old loads gave excessive pressures.



.

Also bear in mind that pressure signs and the signs of too much headspace, are virtually identical. Shooting over a chronograph will tell you if you are at maximum levels, or whether the signs you see are from headspace.

Trying to determine pressure from reading a fired case visually, is not reliable.

I'm a new reloader so forgive me if I misunderstood the reading, but what about signs of propellant around the primer seat, and bright bands around the case head that threaten separation. The are signs of overpressure right? Also case bulge and excessively loud(above normal) report from the barrel?

Smut around the primer is a sign of an enlarged primer pocket. Whether it comes from a gross overload or has merely enlarged because of a (large) number of reloads can be determined by your historical data on that batch of brass.
The ring is more of a indication of headspace than overload.
As posted, a Chrony and a good load book are your friends. When you approach the max velocity for that bullet and that powder, even though you haven't topped out on the load, it means you're getting awfully close to the max for your rifle.
IMO, a Chrony is one of the very first "nice to have" items a reloader should buy.

So the ring is because too much of the case is outside the chamber, so it expands more than the rest of the case?

quote:

Originally posted by medic883:
So the ring is because too much of the case is outside the chamber, so it expands more than the rest of the case?

The case moved forward under the pin impact.
The pressure expanded the case against the chamber walls, locking it in that forward position.
The pressure than (as it built even higher) pushed (stretched) the case head back against the bolt face, when/if it exceeds the tensile strength of the case itself (somewhere around 45,000psi).
The "ring" is the thin spot where the case stretched. This ring is a very narrow one, not to be confused with the wider ring caused by the sizing die mouth.

A couple of other indicators that I do not think have already been mentioned:
1. Reverse bolt face marks on the head of the brass. For example, an ejector mark.
2. Mike the case head before and after firing and compare to the expansion from a load of known pressure, such as a factory load.

quote:

Originally posted by Tailgunner:

quote:

Originally posted by medic883:
So the ring is because too much of the case is outside the chamber, so it expands more than the rest of the case?

The case moved forward under the pin impact.
The pressure expanded the case against the chamber walls, locking it in that forward position.
The pressure than (as it built even higher) pushed (stretched) the case head back against the bolt face, when/if it exceeds the tensile strength of the case itself (somewhere around 45,000psi).
The "ring" is the thin spot where the case stretched. This ring is a very narrow one, not to be confused with the wider ring caused by the sizing die mouth.

Great explanation, Thank you!

The case is driven forward by the primer that
is why peimers will protrude when headspace is
present. The case stays forward until somthing
around 40 kpsi. Then trhe forward part of the case stays and the case stretches until it
reaches the breech. in the meantime the primer
will be forced back into the case. If the case
is oiled it will come back against the breech and stretch forward avoiding the stress ring.

Photos here > www.photobucket.com/joe1944usa

steel rain is a sure sign you've exceeded it.

but, seriously, all the reloading books have pretty decent texts on the matter