I was comparing reloading recipes recently, and was surprised at the extent to which using different wads can affect load pressures. Which led to this question: Assuming you are shooting a gun with modern steel barrels, and using loads within the gun's proof, is there any benefit to shooting lower pressure loads? If a gun is proved to 13,000 psi, does shooting 8,000 psi loads instead 10,000 psi loads (assuming the fps and shot charge are the same) extend the time before a gun shoots loose?

Put another way, is it worth spending extra money on higher quality wads to reduce the pressure in my reloads 1500-2000 psi?

Thanks in advance, Doverham

Given two loads with equal velocity, but one which is 8000 psi vs the other at 13,000 psi, it would stand to reason that recoil should be equal, but wear on bolting and jointing surfaces would be accelerated with the higher pressure load.

Pretty much any mechanical device wears out or breaks quicker as you run it near or beyond its' design limits. Indy and NASCAR cars go like hell, but they sure don't go 200,000+ miles between engine rebuilds.

There are so many variables that must be answered in order to answer the original question intelligently, I'm not going to really try. If the peak pressure pulse is very brief, it may actually cause less wear and tear. Note, I said may.

and, the more you shoot high pressure loads the sooner the wood will crack.

Say what ED ????????

bill

Virginian - I would be curious to hear what are some of the more important variables needed to answer the question.

Thanks, Doverham

bill: the theory is that the weakest part of a gun is the wood. so, the more you stress the wood the sooner it will crack. high pressure loads generate lots of recoil. recoil stresses wood...

If the weight and velocity of the shot of a high pressure load and a low pressure load are the same then the recoil is the same.

No.
No.
No.

100% correct, pressure does not enter in the formula for calculating recoil. Max chamber pressure is but one component of the total barrel pressure. Pressure is applied from ignition, before the load starts to move, until the load exits the barrel. It is of course not a constant, but a curve. If you push the same load (include everything that goes out the barrel, shot wads & powder) to the same velocity then you have done the same amount of work. While the peak/max chamber pressure may vary widely depending upon the burning rate of the powder, the total pressure under the curve for the length of the barrel will for all practical purposes be the same. Thus recoil & the force against both the wood & the shooter will be equal.
A quick perusal of a loading manual shows I can easily find a 1oz load with 1200 FPS velocity @ a max pressure of 10,600 PSI. I can just as easily find a 1¼oz load with 1275 FPS velocity @ max pressure of 8,200 PSI. Fire them both out of a 6-6½ lb 12ga & then tell me which pounds both you & the wood the most.

I believe that running at a lower pressure extends the pressure curve to accelerate the shot to the same velocity. While the total recoil is the same it is extended and feels less with the lower pressure loads. As far as the wood goes I suspect s shove is easier on the wood than a fast rap.

The time required for the load to travel the length of the barrel is on the order of .003 of a second. During this time the movement of the gun in ee Recoil would be on the order of 5/16". Enough inertia is imparted to the gun during this Extremely brief time to continue its travel in recoil. Brother they all give it a Fast Rap. In speaking of powders fast & slow are relative terms. All powders suite for use in a shotgun are Fast in total propellant relativity, some are just a minute bit faster than others.
I have shot mild & pleasant loads using very fast powders & some uncomfortable loads using very slow powders. it all boiled down to the weight i was moving out the barrel & how fast I moved it.

DH, I take it from your post--since modern American guns are proofed at a pressure far higher than 13,000 psi (pushing 20,000 psi)--that you're speaking either of vintage American guns, or of British/European guns with the "standard" CIP proof. Per the proofmaster of the Birmingham Proofhouse, standard CIP proof equates to 13,920 psi as measured by SAAMI transducers. Standard CIP service pressure for those guns is 10,730 psi (versus the 11,500 psi SAAMI service pressure standard for an American 12ga).

Let's say you're reloading based on a formula that tells you the pressure of the load in question is 10,000 psi. I don't know that the gun would wear any quicker, assuming that you never slip up and nudge above the service pressure limit for the guns in question. But those of us who've had our reloads pressure tested by someone like Tom Armbrust know that pressures will vary, sometimes by several hundred psi. So if you don't factor in a sufficient safety cushion, say by reducing your powder charge a bit, you might well exceed the service pressure for which the gun was designed.

Also, if--like many of us--you're working up low pressure reloads for a gun with 2 1/2" chambers using 2 3/4" hulls, you need to remember that the longer hull will produce somewhat higher pressures when fired in a shorter chamber. In Sherman Bell's tests, while most of his loads showed an increase of only a few hundred psi when fired in a short chamber test barrel vs one with a 2 3/4" chamber, in some cases the increase exceeded 1,000 psi. So if you're using 2 3/4" hulls, you need to build in even more of a safety cushion--if you want to make sure you don't exceed the service pressure standard for the gun in question.

While I don't work to develop extremely low pressure reloads--talking 5-6,000 psi or less, as some do--I am careful to build in significant "margin for error" when reloading 2 3/4" hulls for 2 1/2" guns. Factoring in the possibility of a 1,000 psi increase due to hull length, and the possibility of maybe a few hundred additional psi if I drop more powder than the recipe calls for, I like to start with a load with a "book" pressure figure of not much higher than 8,000 psi. Working from that point, I feel confident that I'm not going to end up with anything much over 10,000 psi, and probably well under it.

Of course the other solution is to feed the gun a steady diet of something like CIP standard proof loads, or RST's. The problem with the former is that most of them are field loads with a fair amount of recoil due to shot charge and velocity. RST does offer some nice, soft loads at modest velocity, and 3/4 or 7/8 oz of shot. Because I shoot a lot of targets with vintage or CIP-proof guns, I reload a lot of those--thus giving me both low pressure and reduced recoil. Good for both me and the gun in question.

I believe an intentional higher pressure can be a selected good thing. I feel many low pressure loads seem dirty, or may be more likely to be inconsistent. Anyway, I think cold weather hunting is a good place to consider a higher pressure book recipe.

That pressure spike was one of the things that came to mind when Doc Drew was running the Remington barrel blow up series. Seemingly insignificant swaps could feed a gun more than the shooter anticipated, by quite a bit.

A lot of the old reloading manuals would carry the notation, on low pressure loads: "Not a good choice in cold weather."

If we are talking about plastic wads and plastic hulls, changing the pressure by 1500-2000# is a lot, and there has to be a significant variable going in (amount of powder/shot or type of powder) or coming out (velocity or payload). Offhandedly, I can't recall seeing a list of ballistically similar recipes that can generate that amount of change merely by substituting a wad.

Each gauge has a sweet pressure spot for performance, and it is typically at the high end. That said, I typically load my shells a bit on the light side and use clone wads. The loads go "bang" every time, don't kick too badly, and targets break. That's all I ask for.

From Alliant's web data for a standard light target load:

Using a Rem STS hull, with just a wad swap...




Substituting a Claybuster Fig8 type for a Winchester AA12 in this recipe increases peak pressure by 2,000 psi.

with just a primer swap...





Substituting a F209A for a CCI209 in this recipe increases peak pressure by 3,000 psi.

All perfectly fine provided pressure data is known. But illustrative that willy-nilly substitution is unwise.

To get back to Doverham's original question.

All else being equal, lower pressures put less stress on a gun's jointing than higher pressures. Pressure acts in all directions & higher pressure pushes the case head back against the face of the action harder than lower pressure & this increases stress on the jointing. Given small increases in pressure the difference is likely minimal but it is still there so within reason, lower is to me a good idea for gun longevity.

Read Vic Venters comments in Gun Craft chapter II "Jointing & The Circle" on how modern gunmakers deal with the higher pressures encountered with double rifles.

I agree that assuming equal recoil & gun weight increased pressure provides no or very minimal increased stress on the wood & that you need high enough pressure in a load to provide reliable ignition & combustion in cold weather.

For years my main 12 ga target load has been a 7/8 oz load using PB at a published pressure of just over 6000 psi & it is extremely clean burning & I've never had any cold weather issues with this load

Mike: Yikes!

Doverman,
Newtons third law of motion applies to this issue it reads; " Every force has an equal and opposite force". To quote Burrard ,In the case of the shotgun the force generated equals;" The sum of the total "ejecta" [the combined weight of the shot charge + weight of the wads + the weight of the gases generated by the combustion of a specific powder.]x the velocity that the "ejecta" leaves the muzzle. Burrard discounts the effect of the drop in "ejecta" velocity during its passage up the barrel as being in theory a valid factor but in practice of no real significance.
As stated by others; the lower the velocity for any given charge[ejecta] results in less stress on the action components of any gun and of course the resultant recoil to be absorbed by the shooter.

Simplifying the complex makes it easier to explain, but it does not make it right.