Working up loads: What are the Signs of Overpressure?

[Plastic Cowboy]

Well currently I am working up to max loads for my 500 S&W per Hogdon's website load data.

For you experienced handloaders out there- what do I need to be looking for as I approach the maximum allowed powder charge?

Of course reloading recipes always say to start at 10% below max and work up gradually while looking for signs of overpressure. So what are the signs of overpressure? I don't expect to see any bulging of the case since it is restrained by the cyclinder walls upon firing.

I suppose danger signs may include primers starting to back out, cracks in the brass etc. but I am just guessing.....any help would be greatly appreciated.

(in the interest of everyone's safety I would actually like to see a sticky discussing the warning signs of overpressure)

Thanks in advance.

 

[CSA 357]

cases sticking, flatend primmers, holes in primmers im sure there are more but thats all i can think of

 

[Jet22]

Primers can be hard to read in a handgun. Every gun is a different issue.

A sure sign of overpressure in a handgun is sticky cases. By that, I mean you have to pound the extractor rod with a piece of wood to get the cases out. If this happens, you are way to hot!

What I do with a rifle load is load the same case 5 times and see if the primer pocket is still tight. If the primer can be seated too easily (like with your thumb), the load is too hot. With handguns, this does not work because of the lower operating pressures.

 

[JDGray]

Sticky extraction, hurts to shoot, cylinder wont open anymore, primers fall out after shooting, cant read the headstamp after one shot, just to name a few.

 

[taliv]

large pieces of your firearm flying past your face at more than 1500 fps, is a pretty easy to read sign, although you have to read them very quickly.

 

[Ol` Joe]

The 500 S&W run pressures in the 50K+ range which is what you will find in rifles and not often in pistol cartridges.
The cases should extract easily, not show signs of cracks or splits.
Primers shouldn`t flatten but should have some radius on the edge.
Velocity, if you cronograph your loads, should be at or below the books finding for that load. Not over it.
Case life should be 6 or more fireings - this is my opnion, others may want more or except a fireing or two less.
Case head expansion should be under 0.0005" if you are measuring it.

Don`t use pistol primers in loads for this cartridge, stay with rifle primers. The pressures are too great for them and they could blow or leak. Check with the manual for the one they used to develope the data.

 

[Cosmoline]

If your primers are smoking black holes after shooting, I've found that's a bad sign. Though it does save you time in the decapping stage.

 

[The Bushmaster]

Oh very good cosmoline...I think that might be it....Flattened primers do not indicate over pressure. Bulged cases from semi-autos and sticking cases in revolver cylinders are the best signs of over pressure. Punctured primers are another sign. Primers that have taken on the shape of the firing pin hole (cratering) is another sign of over pressure.

 

[Clark]

John Bercovitz.
He figured out in 1991 that thin steel chamber walls expand more than thick steel chamber walls with the same pressure.
The amount of elastic expansion for hard cartridge brass is ~ 1% ~.
Beyond that, the expansion is plastic deformation.
If the steel goes through more than 1% expansion and contraction on firing, the brass will stick.
This means that, for a revolver, a thin cylinder wall cannot shoot as high a pressure round before the brass sticks to the chamber.
http://groups.google.com/group/rec.guns/browse_thread/thread/4bf75a94cd4d25ed/

That is why the max 357 mag pressures were reduced; cases were sticking in newer thinner revolvers.

 

[TN Shooter]

I would add primer "cratering", too

 

[Doug b]

This has a good article on primers and pressure.



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