doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Why do older guns require low pressure loads?

So, higher pressures=higher recoil, right?
JR

Wrong!!
Heavier payloads and/or Higher Velocities = Higher Recoil.
These factors may or may not be accompanied by Higher Pressures.

So a 1 oz. load @ 1200 fps that generates 11,000 psi has the same recoil as a 1 oz. load @ 1200 fps that generates 7500 psi?
JR

If I get it right, in real life the second load might actually have more recoil, because, while the peak pressure (the maximum level of the pressure generated by burning powder gases - it usually takes place in the chamber, and is the most important value of pressure in terms of safety) of the first load is greater, the muzzle pressure (the pressure level at the moment the load leaves the barrel) of the second load will likely be greater. And muzzle pressure is a great contributor to recoil, working as a jet engine that pushes the gun to the shooter.

The overall pressure (the sum total of the pressure generated by powder from the moment the primer gets off to the moment the load leaves the barrel - that actualy does the job of increasing the speed of the load from 0 to whatever) of both loads will probably be the same.

JR,

Yes, in answer to your example question; recoil will be the same even though the pressures are quite different. Pressure has no bearing on recoil and because of that it is absent from the formula for calculating recoil.

Excessive pressure can & will, however, have a decided effect on how quickly a doublegun may become 'off-face' or loose due to added stress factors beyond intended design limits.

Both pressure and recoil are important factors that should be taken into consideration in selecting suitable ammunition for a given doublegun, but they are separate and distinct and must not be construed as similar. They are not. Either, when excessive, can contribute to premature or even catastrophic failure and unnecessary wear & tear.

Best, tw

Somewhat complicated. If your higher pressure load is using a faster-burning powder, it may recoil LESS than the lower pressure load, because the lower pressure load may use slower-burning powder, and the larger volume of powder should result in increased recoil--although questionable whether the shooter will feel a difference.

I think we have a discussion going on elsewhere which seems to indicate that virtually all shells, regardless of what powder they're loaded with, develop their peak pressures in the chamber and not somewhere down the bore.

So if we compare two loads (taken from published recipes) that are similar but with different payloads, which one might be better for an old gun?

20 ga., 7/8 oz. of shot, 1200 fps, 9,150 psi
OR
20 ga., 3/4 oz. of shot, 1200 fps, 9,810 psi

does using barrel inserts in an older gun help eleminate the possibility of barrel failure. lets say a 16 guage with a 20 or a 4-10 insert? i have often thought about this especially in a lightly pitted damascus barrel.

Payload was really the wrong choice of word here as that would generally be taken to mean only the shot charge. Total ejecta would be more appropriate as this includes shot, wadding & powder gases, all of which are ejected from the muzzle. Increasing this weight or increasing the velocity at which they are ejected increases the recoil. Ejecta weight can be increased without increasing recoil "IF" the velocity is dropped by a balancing amount.
Personally I don't think a really scientific study has ever been performed to establish just what increment of increse or decrease is required for most shooters to actually be able to feel the difference.
MANY GIMMICKS are pushed on this fact, they can not really be proven wrong, But by the same token they can't prove they are right.
Keep in mind though that if anyone claims they can do something to your gun which will both give an identical load an increase in velocity while simultaneusly reducing recoil they are either totally ignorant or a flat out liar.

Safe to say that most people don't have the knowledge or instruments to measure the pressure or recoil. Some die-hards do send their shells away for pressure testing. But then I've read lengthy threads that say having somebody else test your load will only tell you the amount of pressure your shell generates in that person's instument, but not necessarily the pressure within your gun (enter differences in chamber dimensions and, dare I say, forcing cones).

So where does that leave the mere mortal? To make judgements based on the information we have, namely shot weight and published pressures. In the case of factory shells, pressure data may or may not be available, leaving us only with manufacturer's promises of "light" or "for vintage guns".