The Deal With Reloading Data

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Why is there so much variation among reliable sources of reloading data?

“I only use the [insert company name here] reloading manual. It has the correct reloading data.”

I’ve heard that line only slightly more than the classic, “I got this reliable reloading data from the internet.” Both statements are skewed—the latter much more than the former—for different reasons.

What’s a reloading manual? Is it gospel? And, if so, why is there so much variation between the numerous (supposedly) reliable sources? If a reloading manual isn’t gospel, is one set of data more correct than another? All this confusion can drive a guy crazy, especially when starting out.

Ignore The Internet

Regarding reloading data taken from forums, chat rooms and internet posters—I’ve seen enough absurd claims and ridiculous information that I pretty much ignore it all … and it can be downright dangerous. I’m not sure if some folks think they’re funny, or if they feel their guns are capable of withstanding pressures that the rest of ours aren’t, but my simple rule is not to trust internet data.

Looking at the myriad selection of reloading manuals, you’ll notice there can be a considerable difference in charge weights and velocities for a particular cartridge/bullet weight combination. The short answer is this: A reloading manual is a snapshot in time, of a particular test rifle or barrel, interacting with the other variables in the equation, such as primer brand/type and case brand.

The long answer will need some further explanation.

Barrel Variations

Barrel length can, quite obviously, play a role in the velocities attained with any given combination. It’s generally accepted that each additional inch of barrel, in comparison to the test barrel length, will add 25 to 30 fps to the velocity. The reverse is also true; each inch shorter than the test barrel will reduce the velocity by that amount. Take a good look at the test barrel listed in the data and you may find that the company used a universal receiver and a barrel of extraordinary length. That will, logically, equate to a published velocity figure your shorter barrel cannot equal. I’ve seen so many reloaders turn down a load that produced a bug-hole group just because the velocity was 100 fps or so below the advertised book velocity. Odds are, unless you’re developing a load for true long-range shooting, that variation won’t make much difference in the field.

Barrel dimensions can absolutely play a role in the pressures generated by a particular load. I’ve seen barrels that are both “fast” and “slow,” with respects to the velocities and pressures generated in comparison to published data. I’ve also seen circumstances where two reloading manuals, using data developed with bullets of similar profile and bearing surface, reach the upper pressure/velocity limits at radically different charge weights. The two manuals used similar rifles, the same primers and identical barrel lengths, so the logical deduction would point to a variation in barrel dimension.

In testing the data in two of my own rifles, which shared the same barrel length, I found that one of the manuals—which topped off at the lighter charge weight—simply had to have had a “tight” barrel. The velocities obtained in that manual, in comparison to the charge weights posted, didn’t correlate with what I found in either of my rifles, which coincided more closely with the data published in the other manual.

The point here is there are most definitely variations in barrel dimensions and how they react to ammunition. And that is one of the main reasons why it’s so important to start at the bottom of the test data and work your way upward until you find the velocity or accuracy you desire, at a safe pressure level.

Primer Influence

Primer choice is another factor in the differing velocities and pressures. Most reloading manuals will indicate which brand and type of primers were used in the testing, others may not, depending on how in-depth the data is. Make no mistake: Using primers other than the exact brand and type of those used in the test data can and will result in a variation in velocity and/or pressures. If you must switch primers, start at the bottom of the data once again and work up to ensure safety.

Bullet Specifics

Finally, the shape, conformation and construction of the bullet you’re loading can have an effect on your results. Nosler’s reloading manual (which is generously offered online at: Load-Data.Nosler.com) will provide load data for each cartridge by bullet weight. For example, their data for the .308 Winchester and 175- to 180-grain bullets covers eight different bullets. One can easily see the difference in bearing surface between the flat-based 180-grain Partition Protected Point and the 180-grain AccuBond Spitzer boat-tail, and how the two bullets might react differently to the same powder charge. Add in the lead-free options—which are longer than their lead-core counterparts of the same weight—and you can see why the data isn’t all universal.

Pistol bullets can suffer from the same issues; in fact, things can get more complicated when you compare jacketed bullets, plated bullets, lead-free bullets and pure lead bullets. The data certainly changes among the differing bullet types, and in some of the pistol cartridges, the difference in powder weight from the bottom to the top is less than one grain of powder.

Dote On The Details

Here’s what I feel is the most important part of the whole data game: the meticulous records you keep for your firearm. Just as the reloading manual is a lab report for a particular set of gear, your records are the key to loading for your firearm.

Imagine inheriting your grandfather’s rifle or pistol—which is cool enough in and of itself—replete with his book of load data for that particular gun. Knowing what works, what doesn’t, performance notes, game taken, great days at the range and whatnot, it’ll become a veritable treasure for shooters of future generations.

I collect as many reloading manuals as I can in order to get a feel for the variations in the different tests, to better know what to expect from my rifles and pistols, as well as to keep up on the latest powders and cartridges. I actually enjoy poring over the data in these books, and over the years it has changed the way I look at load data—and it also has driven me to record all of my loading sessions. For my guns, my own reloading manual is as important as anything else in print.

Editor's Note: This article originally appeared in the September 2021 issue of Gun Digest the Magazine.

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