M.L. McPherson & Byrom Smalley, January 2002
SMc™: Introducing a New Era
Synopsis: After more than a year of work, the authors – McPherson is a ballistics and handloading expert; Smalley is a retired solid-fuel rocket motor design engineer –have concluded that an optimum chamber design does exist and that during the history of cartridge design, steady progress – based upon evaluation of empirical results – has approached but has not achieved that ideal design. We are sufficiently convinced that we have solved this problem so that, after considerable soul searching, we embarked upon the expensive and time consuming effort toward patenting various principles we identified as being ideal. These characteristics promise superior accuracy and ballistics along with improved barrel life and efficiency and other benefits.
History
As long-time PS readers may know, McPherson has followed
a quest toward understanding if any particular chamber design is inherently
superior and, if so, what it is that makes a good chamber design and,
thereby, what constitutes the ultimate chamber design. To this end,
McPherson has formerly explored unusually short and fat cartridges
and those using spherical shoulder designs. Other than the unusual
difficulties emanating from requisite case forming operations in such
highly shortened designs (refer to an earlier PS article, Breeding
Carbide Toothed Beavers), McPherson has seen no evidence that such
designs have any inherent flaws.
In response to that article, Byrom Smalley, retired Principal Engineer on the Thiokol solid-fuel rocket motor design team, called to suggest that McPherson was on to something. A question posed in that piece, "…does an ideal design exist…?" could, Smalley believed, be answered in the affirmative. Moreover, Smalley believed that by working together, we could identify and develop that design.
Nearly a year later, we had resolved the fundamental issues to achieve an understanding of what really happens inside a cartridge, after primer ignition and before the bullet leaves the muzzle. With that information in hand, it was a simple matter to prove that a specific design was ideal from the perspective of maximizing barrel life, accuracy and ballistic potential for any given case capacity and in any given bore size. We determined that the ideal design should have an internal body diameter at least twice bullet diameter and that the case shoulder interior should be elliptical and lack any significant reverse radius at the shoulder-to-neck juncture (in relatively smaller capacity versions a spherical shoulder works almost as well and has some advantages). Each of these characteristics – ratio of interior case diameter to bullet diameter, body-to-shoulder transition design, shoulder configuration, lack of a significant shoulder-to-neck radius and several other characteristics are covered in our patent application. We then formed a corporation and filed the SMc trademark, for cartridge headstamps and associated marketing purposes. (SMc stands for Smalley/McPherson and is pronounced, SMACK or SMICK – take your pick.)
An Expiation
We must note that, for
various reasons, our decision to patent this invention came only after
considerable debate and consideration – this was not an easy decision
for either of us. On the one side, this path is in direct opposition
to what had come before.