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Does Ammunition Shape Matter?

The age-old question regarding the role of the size of an object in it’s ability to be successful, especially in terms of firearms, has been asked and answered numerous times. However, we seldom look at the shape of an object; in this case, the shape of the ammunition’s casing. C. C. Merideth was the first to question case design when he wrote an article for the July 1946 edition of American Rifleman. His conclusion was that any change to the shape would give only “negligible” differences when compared to making other changes, such as bullet weight and shape. However, his conclusion is not shared throughout the ammo-manufacturing world.
If you are looking to get the most out of your round, or rather to put as much powder in it as is safely possible, then you should fireform your brass to the round’s intended firearm. Fireforming describes what happens to the brass when it is fired from a particular gun. When the gas from the burning powder pushes the bullet out of the case, it also pushes the brass against the gun’s chamber, altering the shape of the case slightly, causing the brass to form to the shape of the chamber.

Wildcatting has been standard practice for advanced shooters for nearly as long as firearms, themselves, have been around. Wildcatting is simply taking an already available round and altering it slightly to create a round that performs completely different than its parent round. This change could mean altering the shape of the case’s shoulder or necking the case to accept a different bullet size. The question, though, is whether or not these minor changes truly alter the performance of the round to any high degree.
G.O. Ackley wrote of his findings following extensive research he and a couple of gunsmiths performed with actual range time. Ackley, using his .257 Ackley Improved and a cartridge named “.25x60mm C.A., set out to prove once and for all if there is indeed an effect from the case design being altered. These two rounds were chosen because they are the same in both caliber and case capacity, with their only differences being the shape of the case. They were so close, in fact, that the capacity difference was only 1.1 grains of water weight, with the higher of the two being the .257 Ackley Improved.
After their extensive testing with these two rounds, Ackley discovered that his Ackley Improved outperformed the .25x60mm by only 3-12 feet per second in velocity. This finding, essentially a zero in extra velocity, can be chalked up to the light 1.1 grain increase of capacity. Essentially, the findings were that changing the case design has nearly zero affect on the performance of the round.
One could argue that changing the neck size and shape could allow for increased powder storage inside the round. The truth is, however, that the extra powder is negligible. In fact, it could even be unsafe to change the case shape enough to truly enhance the round, with such a change causing catastrophic damage to the brass.
Once a case is fireformed to a rifle, you can then begin safely increasing the powder charge. Do so in slow increments, never increasing the powder in one round more than a few percent more than that of the previous round, and always inspect the case properly to ensure there are no case failures present or possible. If you desire to truly become advanced in reloading, you can begin wildcatting rounds yourself as you see the need for such a round in your shooting life.