Shotshell Pressure: How to Avoid Trouble

A clean-burning powder with applications for 12-, 20- and 28-gauge target and field loads, IMR’s SR 7625 is also viable for handgun loads.

A clean-burning powder with applications for 12-, 20- and 28-gauge target and field loads, IMR’s SR 7625 is also viable for handgun loads.
SAAMI has organized US gun manufacturers to adhere to a set of standards for service pressure, and all modern models of guns made in the US are proofed or tested to make sure they withstand these pressures.
Service pressure is predicated on the diameter of the bore (its gauge) and the length of the chamber (in inches). It is understood that the standard gives you a tiny bit of leeway to make a mistake in handloading. If you exceed the service pressure with a load delivering 10 or even 100 fps greater than load data suggests is correct, your load will probably perform just fine and your gun will be safe. For your own sake though, you should consider the service pressure to be an inflexible ceiling.
By saying that service pressure gives you some leeway, I mean that it is purposefully fudged. SAAMI does not discuss this “fudge factor” in public, but it is perhaps as little as 10- to as much as 25-percent above the advertised service pressure. Still, this number is much lower than what is called “proof pressure.”
Alliant’s Herco is a popular and versatile shotshell reloading powder, along with Green Dot and Red Dot.

Alliant’s Herco is a popular and versatile shotshell reloading powder, along with Green Dot and Red Dot.
Proofing is an electro-mechanical process of testing barrels to be sure that they will withstand normal shooting for hunting or competition. It involves firing super-hot, high-pressure shells (heavy shot and slow-burning powders) and then measuring their effects in a barrel. Normally, manufacturers test shotguns with one or two proof rounds and then carefully examine the barrels for damage. You may be certain that any modern barrel has been carefully proofed to keep you safe, keep your pellets in the vicinity of the target and minimize the possibility that any shooter will be injured.
After proofing, barrels are customarily stamped with a particular indentation that indicates they have been tested. Proof stamps are the kind of minutiae that fascinates students of shotgunning, in part because the stamps of foreign “proof houses” are interesting for their variety and intrinsic history. Americans, who are typically more casual with their sense of tradition, commonly neglect such attention to detail preferring instead to concentrate on the shooting characteristics of their guns and loads as tools rather than heirlooms, means to an end rather than the end in itself.

Chances are that you will never see a shell marked for proofing, but if you do, it will bear a conspicuous label (“Danger – High Pressure”) and may, in addition, be clearly marked as a proof load. If you do see such a shell, do NOT attempt to fire it through your personal gun. A proof load generates pressures far in excess of the accepted service pressure.

If you are shooting a 12-gauge Remington 1100 chambered for 2-3/4-inch shells, the maximum SAAMI service pressure standard is 11,500 psi. The SAAMI proof pressure for this popular gas gun on the other hand is achieved with a load of 1-1/2-ounces of shot and measures between 19,000 psi and 20,500 psi, practically twice the service pressure. Not only would repeated firing of that level of pressure damage your gun, but its recoil would probably knock you off your feet.

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