Cartridge Design

Spotting Scope

- Dave Scovill

There has been a lot of chatter on various blogs since the .375 Ruger was introduced awhile back. Most of the chatter is directed at how that case might be necked down to .30, 7mm or 6.5 calibers in an effort to build a super-zapper for big game or long range target work. Overall, most of the projected assumptions regarding velocity with various bullet weights are overly optimistic – some wildly so.

In response to the interest in wildcatting the .375 Ruger, I decided to neck it down to .30 caliber and see how it compared to some of the claims some folks were making for it. As predicted, with some help from the Powley Computer for Hand loaders, a slide-rule device that computes velocity based on basic internal ballistic calculations, results for the .30-375 Ruger fell between the .300 Winchester Magnum and .300 Weather by Magnum. It’s pure physics, albeit the Powley Computer helps avoid the basic math involved, which requires a working knowledge of calculus. In lieu of the Powley Computer, NECO Quick Load is a modern computer equivalent. Some claim the format is outdated, but the basic math is valid.

Sometime after building a .30375 Ruger rifle, Nosler’s cartridges started showing up, which pretty much ended the velocity race in big magnum-type cartridges, especially since the Nosler case has a .528-inch rebated rim and a .547inch case body, and the Ruger case is based on the almost ancient Newton case – .528 inch at the rim and base, with a slight taper to the shoulder. As a result, the Ruger case has less powder capacity than the Nosler design, assuming both are loaded to 3.34 inches overall loaded length (OAL). For reference, the Gunwerks 7mm LRM is based on a shortened 2.5-inch .375 Ruger case. Also, the 7mm-300 Winchester Magnum was once known as the 7x66 Randle (Horacio Randle) and 7mm Super Magnum (Mashburn); limited loading information is available on Load Data.com and in