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.

Randy,

You are correct, however the perception in the shotgun shooting disciplines are strong and hard to break.

When I first came in the early 2000’s I thought one could convince them but to no avail.

It’s 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.

--Johan

Information on Shotshell loading

by Johan Loubser:

Recoil:

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 it’s 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:

First, 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.

True Recoil:

Normal physics still do apply, and in this case Newton’s Third law: For every action there is an equal and opposite reaction.
Formula: Mass of bullet + Mass of powder x Velocity (projectile) = Mass-gun x Velocity-gun.

If 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:

Ergonomics:

Because the shooter forms a part of the “launching platform”, this reaction of the total platform will be as diverse as there are shooters.
One must see the ammunition, gun and shooter as a three part “system” (Combination) forming this “launching platform”. The way these three parts interact and interface, will determine “how” the recoil takes place, and how the shooter will “perceive” or “feel” “experience” the recoil. (Notice the emotional aspects)
Since the body is the heaviest part of the total recoiling mass, which anchors the system to the ground, it has the most inertial resistance. Since the body is soft, that part of the body interfacing directly with the shotgun, will absorb the energy long before the body starts moving (displacing). Thus the maximum absorption takes place in the few inches of muscle and tissue directly behind the butt.
That’s why sometimes small and minute differences in gun design, hold/stance and balance will lessen the effects of recoil, and this will eventually directly determine the level of bruising/punishment, and as such the endurance of the shooter. This endurance-threshold will directly impact the shooters abilities to remain focused and accurate.
This “endurance-threshold” is different for each shooter, and are determined by various aspects of the individual’s body structure re muscle, developed muscle (training), body weight and length (Tall = usually flexible, absorb energy better, softer feel, or short stocky = rigid hard recoil. The psychological make-up/preparedness (training) must also be considered.
Apart from the above aspects, every person has a natural pain-threshold (nerves), and some will be able to endure more than others, before it will start affecting their shooting discipline and results.

Ammunition:

As 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 time’s, and days, to include day to day variation etc.
This can be achieved by altering any one of the components in the above ammunition “subsystem”, which comprises of the primer, case/hull, wad, powder/burn-rate and the weight of the shot.
This effect is the result of the combination and never one of the components only. This can only be properly done by thorough experimentation with different primer/s, cases, crimp /assembly methodology (see section below), wad design/s /make, wad tension (assembly), and the weight the shot.

Important things to remember and do to discern what loads are softer and the importance of measuring the velocity:

Do 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.
This real difference can only be determined by actually measuring the velocity, for the conditions, components and weapon system as used by the reloader/shooter.
When loads are compared and the level of “perceived-recoil” has been determined for a particular shooter, have the velocity measured to confirm that the softer load are actually not merely a slower velocity. Since the formula for Kinetic Energy is half the mass x velocity squared, the shooter will detect a difference in recoil within a few feet per second. Especially the seasoned professional shooters that have developed an above average sensitivity and ability to sense variations between “loads”.

SHOTSHELL DATA

Background and basic Fundamentals.

The 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.
The reason for this is that the Maximum Peak Pressure is reached long before the base of the shot/wad assembly has left the case. (In the case of a CF rifle cartridge, the peak pressure is achieved when the bullet is engraved, therefore the large contribution, as a result of leade/free-bore dimensions on the combustion process. (i.e. bullet/bore interface fit, bullet hardness, bearing surface etc).
The reason for this is that the critical engraving force which is so important to the dynamic combustion process present in a CF rifle caliber is totally absent in a shotgun.
Shotgun and typical straight-case handgun calibers are actually basically the same in their fundamental ratios and dynamics. A shotgun can be described as an oversize low-pressure handgun caliber. That’s why the same powders are used in shotgun and handgun calibers.
This means that the efficiency re ignition and the subsequent increase in pressure, is totally controlled by the integral configuration and assembly of the round itself. These constitute the main inertial mass (shot mass), the initial internal volume (wad design), the dynamic collapse (primary expansion) of the internal volume (collapsible section of the wad), plus the displacing of the internal assembly and the unfolding of the fold/crimp (secondary/Final expansion).
The way this COMBINATION interacts, will determine the efficiency Pressure impulse (Profile and time-base) and the Peak-pressure vs Velocity ratio (P/V). The resistive force, presented by friction in a shotgun is negligible.

Crimping: (Assembly)

This is certainly one of the most important aspects of the Shotshell reloading process.
The influence of crimp on the ballistics is often ignored, and assumed to be of lesser importance than primers and wad make/design.
The fact is that the effect of Crimp-strength can totally overshadow the influence of the other components and parameters. This is controlled by the following:

Crimp depth: Depth setting on crimping machine.
Condition of the case: Material hardness resilience.
Wad: Length, Stiffness and rigidity/flexibility of collapsible section.
Wad Tension: Pre-tension/compression setting on crimping machine.

Some reloader’s 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.

Primers:

It 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.
Again, we must emphasize that it’s all about the particular combination, and whether a change in primer will show a difference in ballistics.
Shotgun primers are very sensitive to firing pin energy. This is due to the proportionally large displacement/deformation that must take place when the primer’s cup is crushed.
It is extremely difficult to pin the data down to a standard one load, where primer X will always deliver higher performances than Primer Z. AAC developed our loads using a standard typical primer. If all conditions are the same, the difference between primers will rarely be dangerous. It is obvious that if the load one is using, are already running at the maximum level with primer X, it would be unwise to merely change the primer and continue loading. This is also true for any change in component or procedure.
Once any component or procedure is changed, the combination will react differently. The proper way to proceed is to reduce the load by about 0.5grain to 0.7grains, and then confirm the performance by measuring the velocity or sensing the recoil/flight time. The reloader can then adjust back to the same velocity/recoil level, by increasing or decreasing the charge mass, or by adjusting to a stiffer softer wad or decreasing or increasing the crimp.

Volumetric loading/dispensing:

Always confirm the “thrown weight’ from any bushing, bar etc on a scale.
There are just too many variables that can influence volumetric measuring, of powder.
These are:
The physical action with which the loading machine is operated.
The atmospheric conditions especially Relative Humidity (RH). This is especially true of single base powders which are very hygroscopic. AAC powders S1000 and S1250 are single base powders; N100 is a double base powder.

Johan Loubser
Ballistician
Ramshot, Accurate Powders

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:

http://www.ramshot.com
http://www.accuratepowder.com
http://www.montanaxtreme.com
http://www.blackhorn209.com

Copyright 2011 by Randy Wakeman. All Rights Reserved.

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