Evidence of the failure of Gehmann’s experiment is that rifle makers soon began dispensing with the double Venturi chambers. Instead they reamed 7×66 S.E. chambers to properly fit the factory ammo. The change did not result in lower muzzle velocities, proving Gehmann’s theory to be just that, a theory. Today we know that 30-40 degree shoulders not only increase room for powder, but also enhance powder burn within the case. This more efficient burn may add the slight velocity increase Gehmann was hoping to get from his Venturi effect, but it also minimizes throat erosion. Finally, the fired cases emerge in proper shape for easy reloading. Physics and the Venturi Shoulder
Speaking of reloading, 7×66 S.E. components are expensive and not easy to find. The design is also not one of the easiest to load yourself, according to experienced handloaders. But with the right combination of bullets, powder, and primer (and rifle, of course), the Super Express is extraordinarily accurate, even by today’s standards. Considering cost and difficulty, a handloader has to be on the lookout for a challenge, not for cost efficiency.
Walter Gehmann invented a bullet to go along with his powerful cartridge. The fast velocities generated by the 7mm vom Hofe called for tough construction to ensure proper terminal ballistics. So Gehmann built his Torpedo Stopring bullet. Somewhat similar to Brenneke TIG and TUG bullets, it features a steel jacket that contains a front core (intended for fragmentation) and a rear core (held together by the jacket and a ring of the jacket forming an internal ring). The bullet nose fragments to damage vital organs quickly while the shank travels deep, penetrating even thick bones in its path. Stopring bullets are out of production. Any controlled expansion or bonded bullets are suitable for modern handloads.
To show you what you can expect to get in terms of output, let’s compare the 7x66mm to the .28 Nosler. The measurements shown in table 1 indicate that Nosler pushed the limits of what would fit in a standard length action even a bit further, utilizing every bit of space for powder capacity. The subsequent gap in case capacity mostly stems from a slight difference in case taper and a bit flatter angled shoulder (30 degrees vs. 35 degrees) in the vom Hofe design. But the relations are almost identical.
(Why the .28 Nosler is Actually Almost 70 years old) — Ron Spomer Outdoors is written by Lukas Schulte for www.ronspomeroutdoors.com