Side Topic: Handloading- Why Are Max Loads Not Always Safe?

I haven't been writing much on handloading recently, but I had to answer a question on my HL list recently, and thought I'd post it here for fun.

I was asked why the maximum listed loads in reloading manuals, supposedly well-researched and tested data, are possibly unsafe in certain applications.  Here's the response-

1) Max loads in reloading manuals are based on pressures achieved in/with their equipment, and subsequent to SAAMI max pressure recommendations for a given cartridge.

2) The pressure testing equipment is also subject to SAAMI specs to ensure it will produce consistent pressures within a certain set of variables.

3) SAAMI pressure recommendations can change over time.

4) Pressure-testing techniques and equipment do change, sometimes radically, over time.

5) When making load recommendations, we are dealing with stochastic (not deterministic) models.  [Example:  2+2=4 is a deterministic model.  yhat = beta-naught + beta-one-x-one + error is a stochastic model.  The error term contains a random factor that we can't control, and changes the yhat each time the equation is run.)

6) The stochastic model for pressure for a given cartridge is thus written in terms of a confidence interval, where there is allowed a small amount of error.  (This error-allowance is critical...the only way to ensure no error is not to load the ammo at all.)  The confidence interval varies based on how much the error term varies in a given situation (i.e. the sample variance), and a constant based on the bell curve determined by how much error we are willing to allow.

7) Rarely, some firearms do not meet SAAMI spec and thus will perform outside the parameters of the testing equipment and produce excessive pressure with a listed safe load.  This is why all load manuals repeatedly insist that we start 10% below the listed max and work up.

8) In addition, certain firearms designs are not as robust as they need to be to absorb full-power, maximum-pressure loads over time.  Thus, rather than a catastrophic failure, we will find a chronological failure with the firearm.  This is often manifest as excessive head space in a rifle, loosening of lock-up in a revolver, or gradual frame damage in a semi-auto pistol, for examples.

9) There are uncontrollable factors based on the skill and quality control of the individual hand loader that can change things in a hurry (i.e. seating bullets too deeply, or not crimping and thus allowing bullets to be pushed into or pulled out of a case during firing, etc.).

So, the likelihood of a catastrophic failure in any firearm when using a maximum listed load is very very small, but still a possibility.  The likelihood of a chronological failure when using maximum loads is still small, but larger than a catastrophic failure.  So one can generally say that load data in manuals is safe, but one must allow for exceptions and follow the 10% work-up guideline religiously to eliminate (as much as possible) the random factor in the hand loading process.

Bottom line- we rolls our dice and moves our mice, and hope nobody gets hurt.

Myth Busting

One of my favorite quotes is from Will Rogers, or Mark Twain, or one of several others, depending on who you ask- "It ain't what we don't know that hurts us, it's what we know that ain't so."

In this spirit, I like dispelling myths. I'll do this on occasion, on various topics. My favorite topics in this vein are firearms and medicine. Here's the first.




Have Lawyers Forced Manual Publisher to Reduce Charges Over Time?

This is a popular sentiment among handloaders. Many will say that max charges listed in their manuals have dropped significantly over the years, and that the cause is company lawyers forcing the changes to reduce liability.

In general, this is a myth.

Here’s why. First, it has been generally established that reduced loads with some powders can be as dangerous as excessive loads. So there is no guarantee that reducing loads will result in a greater margin of safety, thus no legal justification for compelling the reduced loads in the manuals. Additionally, the ammunition business is very competitive. Having max loads listed with your components that show a lower max velocity is not a good way to increase sales, and would be poor business practice. Artificially low charge weights just don’t make logical business sense.

Second, powders have changed to some degree over the years. While some powders are well known to have been tightly controlled as to burn rate over many years (Bullseye, for example…initial lot is over 100 years old, but is still tested against new lots to maintain consistency), others have not. One powder company admitted to Lane Pearce that the control lot for a particular powder was inadvertently lost, and it took some years to stabilize the burn rate of the powder.(1) Other powders have been shifted from their initial stocks of military surplus to commercial versions, including almost all of the IMR line (IMR stands for, “Improved Military Rifle” after all) and much of the Hodgdon line. These shifts mean that burn rates have changed slightly, and the resulting numbers in the load manuals have been adjusted accordingly.

Third, in the past, high-quality pressure testing equipment wasn’t as readily available as it is now. Some loads in manuals from the ‘50s and ‘60s were worked up with traditional pressure signs (flat primers, case web measurements, extraction difficulty, etc.) that are known to be somewhat subjective today. In some cases, loads that had been published for several editions were subsequently tested and found to produce pressures ten to twenty thousand PSI above recommended maximum levels. Obviously, these loads were reduced in the manuals at that point.

Fourth, we tend to notice what we don’t like. In the same article cited above, Lane Pearce found, after looking at six different pairs of manuals, each dated about thirty years apart, that in fact some of the maximum loads had been increased, not decreased.

And fifth, when directly asked, industry ballisticians consistently deny, even when offered anonymity, that lawyers have ever asked them to reduce charge weights below those arrived at by following company policy.

Conclusion: When charges have been reduced in loading manuals over time, they have been reduced for very valid reasons, not because a lawyer said so.


1 Pearce, L. Powder compared: Today’s versus yesteryear’s. Shooting Times, Sept. 1009, pp. 18-23.