Pressure vs. Recoil

Pressure vs. Recoil
Photograph by Terry Allen
By Tom Roster

It has become apparent that there is still widespread misunderstanding concerning the effects of pressure versus recoil, especially among vintage-shotgun owners.

One erroneous belief is that by merely shooting smokeless-powder loads that develop chamber pressures no more than 7,000 psi, such loads can be safely shot in all vintage shotguns—Damascus-barreled or otherwise—made when only blackpowder loads existed and/or when smokeless powder was first coming on. As I have stated in the past, this is absolutely unproven and as such remains guesswork.

Some vintage-shotgun owners guess wrong. Based on the number of damaged vintage guns and personal injuries that I am aware of that have resulted from using these loads in vintage guns, it is clear that using these smokeless-powder loads is not a foolproof, safe practice in “vintage”-type shotguns that have not passed either smokeless proofing in the US according to current SAAMI standards and procedures or CIP-approved nitro re-proofing overseas.

For decades US shotshell manufacturers have warned against shooting smokeless loads of any pressure level in Damascus-barreled shotguns. They print this warning on nearly every box of smokeless-powder loads they produce—and I’m guessing they will continue to do so until some type of definitive destructive test involving firing smokeless loads in Damascus-barreled guns is conducted with the results recognized by SAAMI.

And now for recoil. The principal wearing and tearing agent on shotguns, especially light double guns designed for light loads, is not pressure; it’s recoil. Recoil is what stresses and breaks the metal parts of the action and trigger assembly, cracks the wood, loosens the fit of the barrels and whacks shooters in the face or shoulder.

Recoil is not a function of pressure but of the force caused by the acceleration of a load’s ejecta reacting backward through the weight and design of the shotgun to reach the shooter. Shooting heavy, fast loads in light guns exacerbates this problem. Shooting heavier shotguns with light, lower-velocity loads greatly reduces recoil and thus the stress on both the firearm and shooter.

Pressure, on the other hand, ultimately is an internal ballistic concern regarding primarily the strength of the barrel(s). This varies with the gauge, the strength of the metals used and the wall thickness of the barrel(s). It also goes to any metal fatigue or deterioration present inside the barrel(s) of an old firearm. But pressure is not any part of any equation used to calculate and express recoil.

Let’s be clear: A 10,000-psi 2¾" 12-gauge load of the same shot type, load weight and velocity level is no harder on the barrel(s) of a modern 2¾"-or-longer-chambered 12-gauge gun designed for modern smokeless loads than the same load generating only 7,000 psi. Both are under the current SAAMI or CIP Maximum Average Pressure (MAP) for 2¾" 12-gauge service loads, and that’s all that counts pressure-wise. The difference in pressure between the two is irrelevant regarding recoil, since service-load pressures act independently of recoil.

What has to be watched relative to gun weight is the level of recoil being generated by a given load. For example: Compare two loads developing similar chamber-pressure levels, but one a heavy load with a 11⁄8-oz shot charge driven at 1,330 fps and the other a light 7⁄8-oz load traveling 1,200 fps. The heavier, faster load is going to generate more recoil and overall stress on a shotgun and its shooter. This would be true even if the heavier, faster load developed less chamber pressure than the lighter load. (The latter could be accomplished, incidentally, with shotshell-component and powder-burn-rate choice and/or simply by loading the heavier, faster load in a longer, or roomier, hull than the lighter load.)

Given the above, how should owners of vintage shotguns who are concerned about safeguarding their guns and protecting themselves proceed? First, to combat recoil, always shoot light loads at velocities less than or equal to 1,200 fps. Second, to safeguard the barrels of vintage-type guns, adhere to one of the following tests of a gun’s integrity.

Alternative 1: With a view to shooting modern smokeless loads, take the time and expense to have a vintage shotgun nitro proofed or re-proofed in the UK or Europe in accordance with CIP standards and procedures. Assuming the gun passes proof, be certain to know exactly at what pressure level it was proofed and exactly what the MAP is now for any smokeless-powder service loads approved by the proof house for use in it. Never shoot loads that exceed that MAP.

Alternative 2: In lieu of nitro proofing overseas, have the shotgun proof-tested in the US with smokeless-powder proof loads in accordance with current SAAMI procedures and standards. If the gun passes proof, you can ever afterward fire it worry-free with any modern smokeless, soft-shot-type factory loads or handloads of the correct gauge and shell length that come in under the SAAMI or CIP pressure MAPs at the time of proofing. Since post-production proof-testing of firearms is quite rare in the US, check with SAAMI (203-426-4358, or HP White Laboratory (410-838-6550, for potential testing services.

Alternative 3: Without having US smokeless proofing or overseas nitro proofing performed, the safest course would be to shoot only blackpowder loads in shotguns more than 100 years old. Currently most blackpowder shotshells are handloaded, but Buffalo Arms (208-263-6953, does offer some loaded shells.

Always keep in mind that, to date, shooting so-called low-pressure (less than 7,000 psi) smokeless loads in a vintage shotgun without getting it CIP nitro proofed (or re-proofed) or SAAMI proofed beforehand is not a foolproof, safe practice. Failure to proof-test places the gun and shooter at risk. The record shows that sans nitro/smokeless proofing or re-proofing using current proof levels and procedures, vintage guns and/or their shooters do occasionally suffer the consequences.

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