Why The Difference? Ross Oehms
ing question. “I’m a new reloader who has read a great deal about the subject and there is one item that confuses me. Why are there differences between loading manuals for the same bullet weight and the same powder?” It’s a reasonable question that needs to be answered in
L
Manual producers rarely use highly accurate rifl es to test fi re loads.
some detail to understand why this is so. Thus we should start with our own question: Who, then, produces reloading manuals? First, those who make projectiles – Sierra, Barnes, Nosler, Norma, Hornady, and Speer are typical examples. Second, those who produce powder for reloaders, such as ADI, Hodgdon, Hercules, and Winchester, to name a few. Third, those who make reloading equipment, like Lee and Lyman. Last, individuals who have a long history of writing about reloading and have accumulated a vast amount of data that is worth publishing. Australia’s Nick Harvey is a good example. All of the above are more or less current, but there are others that are much older that have fallen by the wayside as they no longer list powders or projectiles that are readily available. It is a process that is constantly changing in relation to available components. So the fi rst problem our new reloader faces is that a
Case length is an important factor for consistent results.
manual produced by a bullet maker or a powder manufac- turer will quote that X grains of powder in a .270 Winchester case and their own bullet of 130 grains in weight produced 3,000 f.p.s. Our new reloader has absolutely no idea how this fi gure was arrived at. There are only two possible answers. Either the loads were shot in a rifl e chambered for the particu- lar cartridge, or more likely in a “Universal Receiver.” This device is nothing more than a bolt action receiver mounted on a heavy mechanical base that is capable of using one or more barrels, depending on the size of the cartridge base. Usually the pressure generated by a particular load is measurable, although this data is rarely published. It should be noted that both the receiver and the barrel dimensions have to fall within certain parameters as published by the SAAMI specifi cations (USA) or the European equal. There are slight differences. Testing is done under laboratory conditions in a con-
Standard .270 Winchester cases from four different manufacturers. Maximum weight difference is 19.1 grains.
Page 94 October — December 2011
trolled environment. After a suitable number of tests, the results are averaged and the published manual shows that with the nominated components, X grains of a particular powder and a 130-grain bullet weight produced an average velocity of 3,000 f.p.s. If the manual producer does not make cartridge cases they may, or more usually not, tell our re- loader what brand of cartridge case was used. All this is very straightforward but from here on in the waters get decidedly muddy. The possible variations at this stage are numerous even when we change a single component, let alone multiple components. This list includes: the barrel used, powder batch, cartridge case, primer, and projectile. Oh yes, and don’t forget the seating depth. All or any will change the results obtained and we haven’t yet included the rifl e! Powder manufacturers attempt to have consistent
ook at any shooting Web site on the Internet that has a forum and you will quickly run across the follow-
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