Why Shotshell Published Pressures are Meaningless
Above, a vintage Winchester-Western ad from over fifty years ago. Pressure was essentially unimportant then and that hasn't changed one bit since.
Shotshell published maximum average pressures are unimportant, having essentially no value or meaning to the shotshell reloader. All we have to do is review the over 360 pages of a classic work on shotshell reloading, such as Lyman's "SHOTSHELL RELOADING HANDBOOK" 4th Edition. That's a comprehensive, extensive, and well-presented work as far as I'm concerned.
Alright, now despite these over 360 pages of text and data covering a large spectrum of hull types, gauges, pellets and slugs, lead, steel, bismuth, etc. . . . just where is the section on using "pressure" to pick a load? Where? It does not exist. It doesn't exist anywhere in Lyman, a work dedicated solely to shotshell reloading.
Nowhere is the odd notion of "low pressure" or "high pressure" loads discussed, much less defined. Nowhere does it suggest that a 10,000 PSI published recipe is better (or worse) than a 9000 or 11,000 PSI recipe. A peak pressure node averaged out as "MAP" is of zero consideration, importance, or value according to Lyman. It is not even touched upon.
Buy any new box of shotshells, from virtually any reputable, major manufacturer. Now, let's just try to find a pressure number on the new shotshell or somewhere on the box. We won't find it, even the most skilled of us at playing "Where's Waldo?" won't discover the pressure. We can't find it because it isn't there. It isn't there because it is of essentially no value in selecting a new box of shotshells.
There is a very good reason that Lyman doesn't bother with it, nor does any reputable shotshell reloading manual, nor does data from ATK, Western Powders, RCBS, Hodgdon, and so forth. It is of no value, no worth, no consideration. Not one professional ballistician that I know, not Johan Loubser, not Hartmut Broemel, no one in the entire industry including Ben or Dick from Alliant, Ron Reiber from Hodgdon has ever suggested (that I know of) that a shotshell handloader bother looking at a pressure number to select a shell in a nitro-proofed shotgun. None of them, ever. Do we think that this is wonderful coincidence or fortuitous happenstance? It isn't, it is because a MAP value is essentially of no value, worth, or merit when reloading shotshells for modern shotguns.
The reason no major reloading manual suggests that you consider a pressure number, no powder manufacturer or shotshell manufacturer suggests that you select loads based on pressure numbers is blatantly obvious: it is not important.
It isn't important because all published loads are well within guidelines. One load isn't any safer or better than another. One load is not "more within guidelines" than another. They are all usable, approved loads or they don't get published. It isn't pressure related. Load recipes come in exactly two flavors: published and something else. There is no middle ground.
Have you ever wondered why Alliant, Hodgdon, Western Powders, etc., spend all this time, money and effort publishing recipes for us in the first place? The answer is simple: they want to help us to get good results from their products and keep us out of trouble. That's all there is.
Shotshell pressures are all low, there is no high pressure shotshell load that exists compared to other cartridges. It isn't there and never has been.
The .22 Short rimfire has been around since 1857. SAAMI publishes specifications for the .22 Short: it happens to be 21,000 PSI. Spec for the .22 LR is 24,000 PSI. Shotshells typically operate at less than fully half of your old .22 rimfire. Over a century old, the .30-06 Springfield has been around since before most of us were born and before our parents were born-- before our grandparents, in some cases. SAAMI spec is 60,000 PSI for the hoary old gem of a 1906 offering, 600% of many shotshells. It has been around for 105 years. Shotguns and shotshells are all low pressure, very low pressure applications even compared to a .22 Short.
What about pistols? Georgi Luger developed his 9mm back in 1902, adopted by the German army in 1908. SAAMI has a published pressure for the 9mm Luger / 9mm Parabellum (call it the 9 x 19 if you like). It happens to be 35,000 PSI. Shotshells are low, very low pressure applications compared to the old 9mm Luger as well.
Shotshells are the lowest pressure firearms in common use, by far, low pressure even compared to common .50 caliber muzzleloader that hits 25,000 PSI (or more, to past 32,000 PSI) with 100 grains by volume of Pyrodex RS.
After all of these examples, where could anyone get the idea that there is a "high pressure" shotshell? There aren't any in common use, no SAAMI or CIP spec supports such a thing.
After all this borderline fascinating background info, you might be wondering why reloading manuals publish pressures at all for shotshells? Is it just so we can start meaningless and endless threads discussions on the internet or at the clubhouse? Is it a good alternative to political forums, perhaps? The answer is far simpler than even that.
Pressures have been published as a tradition, as MAP pressures are recorded automatically as part of lab testing. The fundamental reason that a pressure number is included in reloading recipes is just to show that the loads have been tested and have been found to fall within allowable parameters. That's it. It is a matter of tradition and proper form and tells us only that the loads have been developed according to published standards, the pressure number included only as a sidebar or footnote for sake of completeness, having no other value.
There are some facets that pressure fans might find interesting, such as the reason for the change from LUP to PSI (speed of data development, accuracy, and LUP doesn't work with steel shot, etc.) It has nothing to with deciding upon a shotshell recipe though, which is merely following published recipes without fail and without substitution.
Johan Loubser is regarded among his peers as one of the top professional ballisticians in the world. Western Powder Company is quite fortunate to have Johan among their talent. Johan does not just work at Western Powder's state of the art ballistics lab-- he designed it. So, I felt it was important to send the above article to Johan for his commentary, the entire content of which is included along with information from his shotshell load guide-- some information that you just won't readily find anywhere else.
You are correct, however the perception in the shotgun shooting disciplines are strong and hard to break.
When I first came in the early 2000s I thought one could convince them but to no avail.
Its a completely emotional issue based on no science at all.
I wrote and included an explanation in the 2004 small loadguide Pages 46 and 47 but nobody did not even notice or care for it.
I highlighted the part about pressure in RED.
Information on Shotshell loading
by Johan Loubser:
This is certainly the most discussed aspect of the shotgun shooting sport, and this is understandably so, because it determines the comfort of shooting hundreds of rounds in quick succession. (See section below on Perceived recoil and ergonomics). Because its such a subjective issue/subject, the conclusions and recommendations are most of the time unfortunately shrouded in confusion, and corrupted by improper comparisons.
First of all we need to emphasize and acknowledge the following important facts:
there is true recoil energy in measured Ft/lbs of the gun itself, and
once the shooter becomes part of the equation, the very subjective issue
of Perceived or Felt recoil.
physics still do apply, and in this case Newtons Third law: For
every action there is an equal and opposite reaction.
different groups of ammunition, with the same shot mass are delivering
the same velocity in a particular shotgun, the recoil WILL be the same.
Perceived or Felt recoil:
the shooter forms a part of the launching platform, this reaction
of the total platform will be as diverse as there are shooters.
can be seen from the formula pressure is not part of the equation. Therefore
the peak-value published in load guides does not really mean
anything. However, Ammunition can be assembled (combination)
to deliver similar velocities = true recoil, with a pressure impulse which
can be slightly altered, having the same total impulse, but over a slightly
longer time base. These changes can them be perceived as being softer.
However, we must again stress the fact that the comparison must always
be fair and clinical (apples with apples) re velocity. A proper average
can really only be determined over a 10 and 20 round test, fired at different
times, and days, to include day to day variation etc.
Important things to remember and do to discern what loads are softer and the importance of measuring the velocity:
not assume the velocity for your conditions is the same as the published
data, even if you are duplicating the exact same combination re components
i.e. the case/hull, powder type, powder charge, shot weight etc as recommended
by any load guide.
Background and basic Fundamentals.
fundamental difference between a shotshell cartridge and a typical centre
fire rifle cartridge is, that the efficiency of the shotshell cartridge
is 100% dependant on the round itself. By this we mean that all the resistive
forces must be generated within the confines of the round itself.
No assistance is provided by the gun.
is certainly one of the most important aspects of the Shotshell reloading
depth: Depth setting on crimping machine.
Some reloaders want to extend case life and they tend to crimp as shallow as possible, and with the least crimp strength possible. However, this practice can be problematic if the improper combination of primer, case, wad and powder is used. Example: If a soft combination is used, it can lead to underperformance, or in extreme cases, bloopers. It is always wise to use a strong a crimp as possible, for any particular load/combination.
is well known that different primers deliver different energy levels.
The way each company manufacturers and formulates the chemical composition,
and configures the hardware (metallic) parts of the primer, all plays
a major role in how the primer will deliver the energy to the powder.
confirm the thrown weight from any bushing, bar etc on a scale.
My sincere thanks to my longtime friend Johan Loubser and the team at Western Powder Company. More information about Western Powders and their extensive product lines can be found at their following websites:
Copyright 2011 by Randy Wakeman. All Rights Reserved.