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Play it safe and update your reloading library.

* Happy is the handloading man with only one data manual! He sees the world of powder charges in metallic cases through a single narrow slit, and thereby suffereth no confusion. He accepts (if he's smart) the dictum that one always begins five to ten percent below "maximum" and then works up from there, watching for any pressure signs. Simple!

But life is not so simple for the fellow with three or four (or eight or ten) data sources. In poking around in this various books, he'll often find "maximums" for a given bullet weight and powder varying from about 3 to as much as 10 grains of some powders. In such cases, which is the maximum, from which he's supposed to reduce starting loads by some percentage? He will sometimes discover that ten percent below one source's maximum is actually over the heaviest charge recommended by another!

Furthermore, if he's been in the game long enough to possess handbooks dating back to or before 1970, he'll find some very mystifying things going on. More of this later, but consider just one example. The 45th Edition of the Lynman Reloading Handbook of 1970, the maximum charge for IMR 4350 with a 300-grain bullet in the .375 H&H Magnum is 82 grains, for a velocity of 2,617 feet per second (fps). In the 46th Edition (1982), the top charge of this same powder for the same bullet is only 74 grains. Incomprehensibly, the velocity shown for this 8-grain reduction is identical, 2,617 fps, in the same barrel length! How can such things be?

A similar situation with this powder and bullet weight occurs in the Dupont Handloader's Guide. The 1971-72 edition lists 82 grains max for 2,670 fps and 52,000 CUP breech pressure, but the 1975-76 edition shows a top charge of only 78 grains, for 2,620 fps and 52,700 CUP! That's 4 full grains less powder for more pressure and only slighlty lower muzzle velocity. Now bear in mind that this is data from the manufacturer of the powder himself, who presumably knows his product better than anyone else, and who certainly has the laboratory equipment and techniques to know what it will do. Nor can there be any question that Dupont is a sober, conservative, and responsible source of loading data. Yet we have not been informed of any change of burning rate of IMR 4350 as drastic as all that; indeed, such a change would easily justify an entirely different numerical designation for a propellant.

If we ignore the older recommendations and confine ourselves to sources published since about 1975 (plus any older ones consistent with these), the original problem remains: how does one establish a "target maximum" charge from which to make that initial reduction for starting loads?

One way to do it is by averaging. The accompanying chart will illustrate how I did it recently for the aforementioned 300-grain .375 H&H bullet with IMR 4350.

It will be noted that the high maximum charge was 79.5 grains (#1) and the low one 74 gains (#4), for a range of 5.5 grains and an average of 77.5. This is a fairly typical spread; I could have chosen other cartridges, powders, and bullet weights in which the variation would be much more extreme. As has been said often and accurately, these differences in no way suggest that any one of the sources is incorrect, but merely that different test guns have been used in compiling the data, and that different men have interpreted it.

Still, that 77.5-grain average does represent the experience of seven different technicians with at least seven different .375 barrels and chambers. How any particular rifle will relate to any of them is unknown. It may accept heavier loads than the average, or even than the most tolerant of the test guns, but the mathematical probabilities are that it will fall somewhere within that maximum-minimum range. Therefore, I believe that that average "max" of 77.5 grains is a reasonable and safe target, and from which I reduced my starting loads by ten percent.

As it turned out in the loading program for which I did the above research, my rifle--an English-built Whitworth--did accept heavier loads than the average maximum at which I was aiming, but not as heavy as the Hornady rifle apparently did.

In the process, I did a simultaneous analysis of two other powders, IMR 4064 and Winchester-Western Ball-Type 760. Interestingly, the extreme spread for the former was 3.5 grains, and for 760 only 1.8 grains from the heaviest to the lightest recommended "max." Presumably, data with these powders was shot in the same test rifles as that for IMR 4350. This would seem to suggest to me that smaller lot-to-lot variations occur in 4064 and 760 than in 4350 (which is consistent with experience), and that 760, especially, can be expected to produce extremely uniform results in my rifle with 760 to agree more closely with those of the various test rifles used in data development. This also proved true in experimental shooting.

One of the implications inherent in such a study, as indicated by the remarks above about IMR 4350 in the old and new references, is that there has been a steady and noticeable trend to conservatism in published maximum loads during the past ten years.
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Author:Wootters, John
Publication:Guns & Ammo
Article Type:column
Date:Jul 1, 1984
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