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

Hi:

I have been cautioned to use "low pressure" loads in my N.R.Davis SXS. What makes a gun to require "low pressure" loads? Is it weak design, inferior materials, poor machine work/ tolerances etc.?

I have read that Damascus barrels are as strong as any despite what many will say. Do these require "low pressure" loads? Some of these old guns have been proofed at very high pressures!

What problems can happen if one does not use low pressure loads in an old gun? Will the action crack, a barrel split will the gun be off face etc? Has anybody ever split a stock on a boxlock if the stock was tight and well fitting via a high pressure load?

TIA,

Franchi

Actually more important to the well being of your vintage shotgun is to keep the recoil within a reasonable range which is often equated to low pressures. In many cases you are shooting a gun that is well over one hundred years old and during that time wood drys out and become brittle, solder on ribs and forend hangers ages and become brittle. It is true that Sherman Bell found that damascus barrels could withstand a tremendous amount of pressure but why push the odds when low to moderate pressure and recoil loads are available.

So you can count to 10 on your fingers. LOL

Franchi, you're talking about an American gun, where really low pressure may not be quite as important as it is on older British or European guns. Our guns were, in general, built stronger--more like tools. That's especially true of guns like Davis, Stevens etc. But back in the 1920's, when Olin came out with the Super-X shell, that raised standard working pressures about 1,000 psi over what they had been previously. So it's a situation of guns not designed for the pressure of modern shells, having suffered some ravages due to age, and metallurgy having improved quite a bit since before WWI. All reasons to hold down pressures at least somewhat, even in older American guns.

When I was 30 I moved a piano on my own, with some blocks and boards I got it into my house. Last year I tried to get it out of my house .I couldn't manage it . I guess its because I'm nearly 30 years older. The answer to your question ,with out going into reams of discussion about metallurgy ,discussions on weather the gun in question had a forged action the quality of the barrel steel,metal fatigue,build quality etc.etal. Its old and was probably never expected to take heavy loads or to have lasted so long.

This is a gun from the late 1940's No problems were visible until the locks were removed. Wood will only take so much punishment....



Pete

Thanks for the answers! I like Mike Harrrels answer!

When I was a youngster, a nice older gent would take me hunting. He had all of his fingers on his left hand blown off by a shotgun while hunting one day.

He had no idea as to what happened but he was sure of the result. The gun was not plugged with anything when he fired it. It just blew up! I never forgot this "lesson" about shot gun operation and to this day, I try to remain on the cautious side!

Franchi

Older shotguns require lower pressure loads for the same reason that older men need VIAGRA -- some important parts have weakened over the years, and aren't as strong and hard as they once were!

Pressure will not crack stocks, but excessive pounding will, especially if the wood is old, brittle, oil soaked, or all of the above.

Pressure will exert more force upon bolting surfaces, hinge joints, and the receiver itself. Barrels in good condition will usually take a surprising amount of pressure before they fail, but one failure can end your shooting career in a split second.

Turn of the century guns were built of milder steels with less refined metallurgy, alloying, and quality control than is common today. They were built to handle the loads in common use at the time. Most importantly, some action designs are better able to handle a multitude of shots at maximun design pressure before they wear or break. If we could find a new in box N. R. Davis and a new in box Winchester model 21 and began firing the same 12 ga. RST low pressure loads in them, most everyone here would bet large money that the Model 21 would still be tight and sound when the Davis was worn out. Jump up to standard pressure loads, and the Winchester will hardly hiccup while the Davis will slowly be pounded to death. Once the wear starts and bolting surfaces are peened and deformed and the gun gets loose, the rate of additional damage will accelerate. Certain designs are just better than others. Cheap guns of poor design and materials just don't stand the test of time unless they spend most of that time sitting in a closet unfired.

If your Davis was properly put back on face and you use conservative loads in it for hunting, it will probably outlast you.

Jerry, I was not aware you'd been buying guns that have barrel droop!

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".

I have wondered about this, and how much difference it makes. I do use a set of chamber-mates in a 10 gauge damascus Baker to shoot my own low-pressure #7625 12ga. reloads. (I don't have 10 gauge reloading tools). It is clear these same 12 ga. reloads recoil less in the 10 gauge, than they do in a 12 bore. I now load the shells intended for the 10 gauge with a bit more powder, but stay under 7,000 psi (I think/hope).

In my case, the UNKNOWN is whether factory 12 gauge ammo would be of safe pressure in the 10 gauge damascus barrel. I'm not inclined to experiment/test. Perhaps some engineer could calculate the ratio of bore volume change resulting from firing 12 gauge shells in a 10 bore.

JERRY

I think chamber dimensions should not be of much significance. If I recall correctly, the difference in chamber diameter, standard American 12ga vs British 12ga, is .002"--so little that Brit hulls work in Yank doubles, no problem, and vice versa. And a bunch of people, from Burrard and Thomas on up to Bell, have played enough with long shells in short chambers to show that, to borrow a phrase from the late Michael McIntosh, that's a fairly friendly troll--as long as the pressure is safely within the parameters for the gun in question. Increased pressure because of the long shell/short chamber combination seems to run in the vicinity of virtually none to a few hundred psi. In other words, not enough to hurt as long as you leave yourself enough cushion. And as long as the gun in question does not have one of the older forcing cones that approaches a right angle rather than a taper.

I truly wish I could now recall the source to give proper accrediation but I read many years ago from a source citing a major ammunition makers ballistitions as saying in shotguns the pressure was essentially built within the shell. Within the normal parameters of allowable tolerences rtc the gun itself played only an insignificant role in determining the pressure of a load. Most pressure, even so, are bored to minimum dimensions so any factor the gun dimensions play would be more apt to produce lower pressures than higher. Actual bore dia's can of course vary the pressure down the bbl, but this has virtually no affect on max chamber pressure.
This is of course not true in the case of rifles, where bore & chamber dimensions can play a most important role in developing pressure.