June
2000, M.L. McPherson, Ballistician
With contributions from Mr. Robert
Byrom Smalley, Jr., Rocket Scientist
Synopsis: Despite more than 150 years of the self-contained cartridge, we have seen precious little documentation covering research into case design optimization. New information – gleaned from the disparate design disciplines of solid-fuel rocket engines and, of all things, 2-Cycle engine exhausts – suggests that a relatively short, fat case with a specific shoulder design may very well be ideal.
Owing to the difficult nature of this subject, I have erred toward too much detail; therefore, the following article contains a measure of deliberate repetition. Please note, that as the primary author, I (M.L. McPherson) must take responsibility for this text, while Mr. Smalley and I have worked together in an effort to fairly represent this subject, we do not necessarily fully agree on the importance or accuracy of every aspect discussed in the following text. Furthermore, I am happy to take full responsibility for any errors, conceptual, factual or otherwise. Finally, please, bear in mind that our goal is only to present the details of a basic argument….
Mr. Smalley (who prefers the moniker, By) retired as a principal engineer in solid rocket engine design, a field with definite relationships to cartridge design. As a hobbyist, he participated in the design of several World Record holding model airplane engines. Specializing particularly in exhaust system design, By designed and optimized an exhaust system based upon an idea originated in the late 1800s. He thereby helped design a 0.049 cubic inches, 2-Cycle engine with world-beating size- and weight-to-horsepower ratios, which propelled a scale airplane to 120 mph! Later, we will see the surprising relationship which that work has to one aspect of optimizing cartridge design.
I am not shy about theorizing; sometimes that is good. My recent forays into discussion of case design seem to have been of that ilk. Regarding my speculation on, "Ultimate case design…" I have heard from my friend, Bob Bell (respected, long-time Handloader's Digest Editor), many PS readers, two reamer manufacturers, one gun manufacturer and now a genuine rocket scientist, Mr. Robert Byrom Smalley, Jr.
Numerous responses from variousPrecision Shooting readers suggest that this subject is of general interest. In his letter, Mr. Bell noted that a half-century ago, "There was considerable debate among shooters along these same lines…" He kindly added that such debate was "…without any firm direction or any comments showing the advanced thinking that your articles suggest." He goes on to offer evidence that, for most shooters, the entire issue amounts to much ado about almost nothing – existing designs are so good…(emphasis, mine). Nevertheless, I would contend that better is better and progress toward that unobtainable goal "perfection" is at the heart of the pursuit of Extreme Rifle Accuracy.
During various telephone conversations, By, confirmed that I am on the right track. While an overall optimum case design may not exist, it is possible, at least in theory, to optimize case