Reloading Data Variations
By Gary Zinn
Anyone preparing to develop a new reload for a rifle or handgun cartridge should generally consult two or more load data sources before committing to a particular recipe for the cartridge and bullet in question. There are several parameters to be considered, the most obvious of which is comparison of the maximum muzzle velocities (MV) achieved by alternative powders. This is not a no-brainer, because load tables from different sources typically show different results with the same powder.
How much variation is there among load recipes for particular cartridges and bullets? Sometimes not much, but usually enough that the reloader may be left somewhat uncertain about which recipe is best. One may wonder why I recommend checking multiple sources before settling on a load recipe, for it would be simpler to choose one source and go with it, thereby avoiding potential confusion.
There are four basic considerations that lead me to advocate checking two or more sources of data on any load. (1) The powder and charge weight that gets the absolute maximum MV may not be the most accurate. (2) Some powders are markedly more efficient than others. (3) Some load tables may be conservative (or optimistic) regarding maximum MVs attainable. (4) There may be anomalies in the data for particular loads (rare, but it does happen). Studying load data from at least two or three sources can be helpful in discerning and dealing with any of these situations.
(1) Velocity versus accuracy
The Nosler Reloading Guide data tables are organized in a manner that illustrates the first situation listed above. The tables for rifle cartridges show the MVs attained by a maximum charge of several powders, plus velocities yielded by charges 2 and 4 grains below the maximum, for various Nosler bullet weights. (Nosler handgun load tables show the same, except the reduced charges are generally 0.5 and 1.0 grains below maximum.) In addition, Nosler notes the charge weight of each powder that gave the best accuracy in their testing, and the powder that gave the best overall accuracy.
The table for .308 Winchester loads with a 150 grain bullet is an example. It shows load data for 11 powders, only two of which gave best accuracy with a maximum charge weight, according to Nosler tests. Two powders got best accuracy with charges 2 grains below maximum, while the remaining seven were most accurate with charges 4 grains below maximum. The powder that gave the best overall accuracy ranked fifth in maximum MV of the 11 powders, 110 fps below the maximum velocity of the strongest powder. Similar patterns may be found for other cartridges and bullet weights in the Nosler tables.
The four grains below maximum loads generally were between eight and nine percent below the maximum powder charges of the respective loads. This suggests that the most accurate loads for some rifle cartridge / bullet weight combinations may be with charge weights well below the maximum charge. In other words, there is often a tradeoff between maximum velocity and best accuracy.
(2) Powder efficiency
I measure powder efficiency by calculating the MV per grain of powder used. In the Nosler .308 Win. / 150 grain bullet table, the most efficient powder generates 65.2 fps MV per grain of powder (for the maximum load), while the least efficient powder gets 60.1 fps per grain. In this case, the difference is manifested by the most efficient load getting 2997 fps MV from 46 grains of powder, while the least efficient load gets 2842 fps from 47 grains, a 5.4 percent difference in velocity from similar amounts of powder.
In other cases, a more efficient powder will use a smaller charge to achieve a given MV. This means more loads per pound of powder can be produced. For instance, in the Hornady Handbook .308 Win. / 150 grain bullet table, 43.3 grains of the most efficient powder yields 2700 fps MV, while 48.9 grains of the least efficient powder are needed to achieve the same MV. One could load 161 rounds from a pound of the efficient powder, but only 143 loads per pound of the inefficient powder.
(See Efficient and Inefficient Reloading Powders for a fuller discussion of powder efficiency over a range of rifle and pistol calibers.)
(3) Conservative load estimates
I used four sources for the examples presented in this article. These include the Hodgdon 2017 Annual Manual, Nosler Reloading Guide 8, Hornady Handbook of Cartridge Reloading (10th edition) and Lyman Reloading Handbook (49th edition). There are, in addition, several other reliable printed or online load tables available. (I count nine additional load manuals or reliable online load data sites, from firms that make bullets, powders, or reloading equipment.)
Among these four reload data sources, the Hornady Handbook often tends to be conservative in the maximum MVs of the loads listed. Not all Hornady tables are conservative, but it happens enough that I am not surprised to see it. For instance, the Hornady handbook lists 13 powders for .308 Win. / 150 grain bullet loads, five of which achieve 2800 fps maximum MV with a specified powder charge and eight getting 2700 fps. Here is how the Hornady table compares with the other three sources.
Hodgdon table - 6 loads over 2900 fps maximum MV; 5 loads between 2800 - 2900 fps maximum MV; 5 loads less than 2800 fps maximum MV
Lyman table - 4 loads over 2900 fps maximum MV; 7 loads between 2800 - 2900 fps maximum MV; 3 loads less than 2800 fps maximum MV
Nosler table - 3 loads over 2900 fps maximum MV; 7 loads between 2800 - 2900 fps maximum MV; 1 loads less than 2800 fps maximum MV
That the Hornady data is sometimes more conservative than data from other sources is not a knock on the Hornady book. I usually use it as my first reference when studying the prospects for a new load, for I am confident that the Hornady data gives safe, efficient and usually quite accurate loads. I have several pet loads that are at, or very close, to loads listed in the Hornady Handbook. If I want a load with more velocity than is indicated by the data in a Hornady table, though, I look to other sources to identify loads that may quote higher MVs.
(4) Load data anomalies
Nosler load data is developed using universal receivers and (with a few exceptions) 24 or 26 inch test barrels. Barrel brand and length is clearly stated for each cartridge in the manual. Hodgdon load data (with a few exceptions) is typically developed in 24 inch test barrels, presumably in a universal receiver, although this is not stated. Lyman load data is developed using a mix of test barrels (usually 24 inch) in a universal receiver and production rifles (Remington 700, Weatherby Mark V, etc.) with various barrel lengths and actions. Hornady load data is developed entirely in typical production rifles, so the barrel length and action varies widely from cartridge to cartridge. Obviously, these variations in testing protocol will result in quite different measured MVs.
All of these sources quote load data for typical bullet weights in each cartridge, but the bullets are different brands and types. Some bullets are harder than others and have different bearing surfaces. This will cause significant variations in velocity, even when all other factors are identical. Usually, other factors (brand of brass, primer, powder lot) are not the same, introducing further variables. The sum of all these variables can result in very different MVs, even with the same bullet weight.
I stated earlier that load data anomalies are rare in tables from reputable sources. Quite by happenstance, there is one in the .308 Win. / 150 grain bullet tables I used for this article. The Nosler table lists a maximum load with 46.0 grains of Alliant RL 15 powder, at 2958 fps MV (universal receiver, Lilja 24 inch test barrel, 1-10 inch twist, Nosler bullet, Federal 210M primer, Nosler case). I was cross-checking this load against RL 15 loads in the other sources and noticed that the Nosler load quoted the highest MV with the lowest powder charge, compared with load specs from the other sources.
I went directly to the Alliant load data site, where I found the relevant maximum load quoted as 49.0 grains of powder for a MV of 2919 fps with a Speer 150 grain SP bullet (22 inch barrel, CCI 200 primer, IMI case, no other details supplied). This was much more consistent with the loads shown in my other sources.
I can only speculate why the Nosler data is so different. These differences could be due to variables in testing methods, or perhaps something like a transcription error in compiling the Nosler load data.
In this case, using the Nosler data to work up a .308 Win., 150 grain bullet load would cause no danger, for 46 grains of RL 15 powder is lower than the maximum powder charges shown in the other sources. Nevertheless, this illustrates why it is S.O.P. in reloading to always check loads across two or more sources.
While gross data anomalies are relatively rare in load tables from reputable sources, I am not nearly so confident about load data from what I think of as casual sources. There are a number of internet websites and forums that post load recipes developed by individuals, including originators of the site or forum in question and, sometimes, by voluntary contributors. I have seen some very strange load recipes on such sites, so I never use them. I see no point in using such recipes, for there are plenty of reputable sources of load data that will not get the user in trouble.
Ranges of variability in load data
I chose two popular cartridges and loads, .308 Winchester with a 150 grain bullet and 9mm Luger with a 115 grain bullet, to convey a sense of the variability of reload data. I scanned the primary load data sources mentioned above, extracting maximum load data for the powders that appeared in at least three of the four sources. Here is a summary of the results.
Either three or all four of the sources listed .308 Win. / 150 grain bullet loads with five of the same powders. The maximum powder charge weights among these ranged from 44.5 to 49.0 grains; the maximum MVs ranged from 2700 fps to 2937 fps. The spread between both the smallest and largest charge weights and the slowest and fastest MVs is 9% (rounded).
Either three or all four of the sources listed 9mm Luger / 115 grain bullet loads with eight of the same powders; one powder, though, had so little variation among the tables in which it was listed that it can be ignored. The maximum powder charge weights among the remaining seven ranged from 4.1 to 8.7 grains. The maximum MVs ranged from 990 fps to 1253 fps. The spread between the smallest and largest charge weights is 112% and between the slowest and fastest MVs is 27%.
Another type of variability among loads is the relationship between powder charge weight and muzzle velocity. In an orderly world, the smallest powder charge would yield the lowest MV, while the largest charge would produce the highest MV. This does not dependably hold true in the example data. Low charge weight - low MV and high charge weight - high MV consistencies occurred in loads with three of the five rifle powders and three of the seven pistol powders.
When I began reloading, I recall being somewhat confused and frustrated by the variabilities and occasional inconsistencies I found among load recipes. It took me some time to understand that the variability is really more an opportunity than a problem. If I want to quickly develop a safe, no fuss, no muss rifle load, I will choose and cross-check a conservative recipe and go with it.
If I want to tune a particular load for top accuracy in one of my rifles, I start with a recipe that has a wide powder charge and MV range. I then work up and fire enough test loads, with small powder charge increments, to find the "sweet spot" of optimal accuracy in my rifle.
If I want a high velocity load, I will pick a recipe that promises high MV with maximum powder charges. I then use incremental test loads that work up to the maximum, watching for any signs of the recipe producing excessive pressure in my rifle.
When reloading handgun cartridges, I have found that load development boils down to three concerns. I develop reloads for my autoloading pistols that are strong enough to cycle the action without fail, but that are not so strong that they are jarring to shoot and hard on the pistol.
In developing loads for revolvers (and rifles chambered for handgun cartridges), I tune my loads for consistency in group size on the target. Most of my pet load recipes for handgun cartridges use less than maximum powder charges.
(As an aside, my favorite load for my .223 Remington AR-15 is one that cycles the action every time, and ejects the empty cases into a remarkably small area. It is not a maximum charge load.)
The third concern that I incorporate into my preferred handgun loads is economy. I shoot a lot of 9mm and .38 Special ammo at the range, so economy is important to me. My pet loads in these two calibers feature small charges of highly efficient powders, so that I get a lot of loads per pound of powder. The 9mm charges are heavy enough, however, to reliably cycle my pistol and I mostly use the lightest charge weight .38 Special loads that get consistent groups.
Variation in load data from different sources is a fact of life for reloaders. We just need to accept it, learn how to deal with it, and use it to our advantage to optimize our loads for our needs and preferences.
Copyright 2018 by Gary Zinn and/or chuckhawks.com. All rights reserved.