batches so that each container of powder is exactly the same as the last one. Unfortunately, there are slight variations between batches and this will affect the burning rate of a particular powder. You should reduce developed working loads when you change batches but I suggest that few re- loaders do so. Slower powders are usually greater in charge weight than faster ones. The terms faster and slower refer to powder burning rates. Manuals usually offer a range of powders for each bullet
weight. If you read the data it becomes obvious that faster powders are usually associated with lighter projectiles and smaller case capacities, slower powders with heavier types. As a general rule, heavier projectiles will produce better ve- locities when propelled by slower powders. The humble cartridge case is another source of consider-
able variation. First, you have to consider the metallic struc- ture of the case. Some are considered to be softer than others in relative terms, conversely others are said to be hard. The difference that has the most effect is the actual thickness of the case walls. Thicker case walls mean less internal capacity. Thus, when Y grains of powder is ignited in a case with less volume than another brand, the pressure must increase. This in turn will normally create higher velocity. You easily can prove this by weighing the same types of cases from different manufacturers on a powder scale. When developing a load you should use only new
cases. The reason for this is simple: Cases fi red many times tend to work-harden the brass, both through the act of fi ring and many trips through the reloading dies. The area most affected is the neck of the case. It loses its elastic tendencies and fails to grip the projectile with the same force. Eventu- ally you can feel this when seating a projectile in the seating die. This lack of “grip” allows the projectile to exit the case easily when fi red; thus the pressure is less and so is velocity. Annealing of the case neck will restore the ductile properties of the brass. The process is not diffi cult and it will extend the usefulness of brass cases. There is some difference of opinion about the role of
primers and their effect on pressure within a particular car- tridge case. Suffi ce to say there is some variation between brands and types. Manual producers rarely name which type of primer was used during testing. Perhaps the main reason why manuals are updated and
change is the vast numbers of new projectiles that appear with great regularity. It is simply diffi cult to keep up with the new offerings in the marketplace. Older types are quietly dropped out of the range in the struggle for market share. To be fair, the really good projectiles now available are a much better selection than, say, ten years ago. In this mix we also have pure copper projectiles that once would have been unthinkable. Different projectiles have a huge infl uence on the pres-
sures generated when a powder charge is ignited by a primer. The most obvious variation has to be in the length of the bear- ing surface that will actually contact the barrel rifl ing; this difference may be evident only when measured. The longer the surface the greater the friction for the powder charge to overcome. This in turn is also a function of the hardness of the projectile’s jacket. Longer projectiles also need faster barrel twist rates to provide accuracy, another reason for increased pressure and hence velocity. If a projectile manufacturer
Whilst the bottles are the same the batch numbers are different.
changes the jacket hardness for any reason, it is highly un- likely that the average reloader would ever hear about it. So our new reloader might not even consider that chang-
ing projectiles, or for that matter any other component, has an effect on the manual’s velocity. Normally, manuals will publish data indicating the maximum overall length of the loaded round. This is important for several reasons. First, the round has to fi t into the rifl e’s magazine. In some rifl es the best accuracy is achieved by seating a particular projectile close to the lands of the rifl ing, and this length may exceed the length that will fi t in any particular magazine. If you seat the projectile farther out of the case there is
room for increasing the powder capacity, but the downside of doing so is that the distance the projectile moves before engaging the lands is reduced and this will increase pres- sure. If the load is developed in the normal manner with the projectile seated in touch with the lands, this pressure rise should not be a problem. Despite all of the possible variations up to this stage, we
are now going to consider what happens when a particular cartridge is fi red in one rifl e. For sporting arms the varia- tions in dimensions are specifi ed by SAAMI or its European
Different powders will affect the results obtained.
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