proof load

Proof Loads For The Total Beginner

You might have heard mention of something called a proof load in reference to what your gun (or any gun really) can take in terms of stresses. The term isn't solely for firearms; it's used elsewhere to determine the strength of something such as a metal bolt used to join two pieces of material.

It's actually a good bit of information to know about in case you plan on shooting any Plus P ammo or hot handloads, so let's dive in and learn a bit more.

Proof Load Applies To More Than Guns

proof load

A "proof load" can be applied to much more than guns, as it's a measurement of how much stress an object can take.

The most basic definition if proof-loading a bolt, let's say, is the maximum amount of tensile force that can be applied to it until the bolt plastically deforms. In other words, what sort of stress an object can take until it warps.

Most materials have a certain amount of elasticity, meaning they can take a certain amount of stress and go back to their normal shape. However, there is also a point at which the stress is too much for the molecular structure to bear. The material doesn't break, but irreparably warps. That's plastic deformation.

The proof load, therefore, is the upper limit of a material's elastic range or the range of stress it can endure before being damaged.

Gun Proof Test

proof test

Now, in firearms, the stresses and strains it will endure isn't in terms of foot-pounds or Newtons of force, per se, but rather in units of pressure. Specifically, chamber pressure as that is what gun proof loads measured in a gun proof test.

Sufficient chamber pressure will cause the firearm - be it a semi-automatic or revolver - to deform, either by warping the chamber or cylinder, the cylinder crane or barrel throat.

Planning on shooting the hot loads in your magnum revolver? You better know what it can handle first.

How Are Proof Loads Determined?

proof loads

In a proof test, a proof load is handloaded to a maximum pressure that the firearm should be able to take without causing plastic deformation, which is usually about 25 percent more pressure than the maximum pressure of the cartridge the gun is chambered in. The gun is loaded with it and fired twice. The gun is then inspected thoroughly to determine if it has been damaged in any way.

In the broad strokes, if it takes the proof load without any issues, then the gun is approved for sale and given a proof mark. This is a stamp confirming that it is a properly working pistol and is therefore safe for use.

A semi-automatic gets two test shots and gets sent on its way. A revolver needs a proof test on every cylinder before passing inspection.

However, it's a bit different in CIP member countries. The CIP - or the Commission internationale permanente pout l'e'preuve des armes a a feu portatives and try saying that ten times fast - has a procedure that all member states must follow. After a gun is made, it's sent to a national proof house for testing. Each member country has one or two proof houses that does all the proof load tests for all guns made in that nation.

Germany, incidentally, has seven but then again many guns that wind up in holsters and on gun belts are made there, so it makes sense.

If a gun passes (25 to 30 percent more than the CIP-defined maximum pressure loading, so +P++) it gets the official proof stamp of the proof house it was tested at and is approved for sale.

Granted, there are only 14 CIP member nations, 13 of which are EU countries and then you have the United Arab Emirates. However, if you buy a firearm made overseas, you'll probably find the proof mark on it.

Basically, it establishes that a gun can take the stress of firing and thus is safe for general use.

Why Should I Be Aware Of Proof Loads?

proof testing

Why should you be aware of proof loads?

Well, if all you do is shoot standard pressure factory ammo, you really don't have much to worry about for the most part.

The folks who do have to watch out are the ones with a black powder reproduction revolver. If you bought a SAA, Remington New Model Army or Schofield clone, you need to be concerned about the proof loads because you can get yourself into trouble in short order.

Certain chamberings in those firearms have high and low pressure variants. You CAN use smokeless powder in a black powder firearm, but the smokeless load needs to be a lower-pressure loading for cowboy shooting.

Big bore pistols among the cowboy guns will be in .45 Colt, though a few are chambered for .357 Magnum and even the odd .44 Magnum. However, these guns are usually proofed for the low-pressure cowboy loads. Modern hot loads of .45 Colt (usually labeled +P) are basically .44 Magnum charges in a bigger case, and generate up to 25,000 psi. The .357 Magnum and .44 Magnum rounds generate more than 35,000 psi. Those loads can destroy the gun if you shoot it, and should be reserved for guns like Ruger Blackhawk and Freedom Arms revolvers that can take it.

Therefore, if shooting a cowboy revolver, you'll want to read the owner's manual carefully and find out about the proofing the manufacturer does. Use the cowboy ammunition or the standard pressure loadings that the gun is built for. You won't have much trouble with .38 Special and standard .45 Colt, but you probably shouldn't go beyond that.

For the person carrying a modern pistol, you should consult the owner's manual and learn about manufacturer proofing if you plan on carrying or shooting any +P ammunition. Most simply say not to use +P regularly or not to at all, so it may take some digging.

Sam Hoober  

About The Author

Born in southeastern Washington State, Sam Hoober graduated in 2011 from Eastern Washington University. He resides in the great Inland Northwest, with his wife and child. His varied interests and hobbies include camping, fishing, hunting, and spending time at the gun range as often as possible.

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