One look at the .375 H&H’s long, sloping case, and there’s no surprise that considerable efforts have been made in improving the design. A quick perusal of A-Square’s Any Shot You Want, Barnes Reloading Manual #3 and P.O. Ackley’s Handbook for Shooters and Reloaders shows seven versions based on the H&H case alone. If you’re willing to include the Rigby, WSM and ’06-based sizes, there are at least six more listed in just these three books. Notable characters like Border Patrolman Bill Jordan, Kodiak’s Hal Waugh and Warren Page all carried improved .375s and sang praises on their performance. The popularity of the recent .375 Ruger is again proof that the desire to improve the .375 H&H is alive and well. Smitten by all this endorsement, I had a Model 70 Classic Stainless opened up to the 40-degree Ackley version, thinking it would bring me one step closer to the ultimate do-it-all rifle. In the end, I was not convinced this particular conversion was worth it.

The 40-Degree Shoulder

Pushing the shoulder out to a steep angle and removing the bulk of the taper in a cartridge case should improve it. This action increases case capacity and therefore velocity, which in turn flattens trajectory and increases downrange energy. Not as dramatic but perhaps more important, benefits are ascribed to a minimal taper, steep shoulder case design. The parallel walls of an improved case grip chamber walls tightly, theoretically reducing bolt thrust and case material flow. Decreased bolt thrust increases safety margins (or handles higher pressures if that’s what you’re after) and reduces shock and vibrations in the receiver that, in theory, again improves accuracy and consistency. A steep shoulder also helps to minimize case material flow, prolonging case life and establishes headspace better than a sloping shoulder. Finally, a short, fat powder column is said to burn with better consistency and efficiency than a long, skinny powder column.

The degree to which the 40- degree Ackley version in my rifle provided these improvements is debatable. The ratio of length to shoulder diameter is still approximately 5:1 for the full-length 2.850- inch case, which is twice the 2.5:1 ratio of the 6mm PPC and more than an unimproved ’06 case. While the improved chamber did not appear to improve the rifle’s accuracy, the steep 40-degree shoulder did serve to eliminate case stretching during the firing and reloading cycle, a behavior common to the standard version. Brass life was excellent and no particular difficulties were encountered in reloading. Factory loads fire-formed into immediately usable brass as did reloads with 210-grain cast SWCs over 20 grains of Unique. Redding stocks die sets and individual dies for the .375 Improved, 40-Degree Shoulder (item 84440 for the standard two die set and 80440 for the deluxe set), and my standard Redding set functioned perfectly. RCBS also lists a G-Series die set 56453 for the .375 H&H Improved 40 Degree.

On one hand, I was able to achieve 2,700 fps with a 300-grain bullet, but any theoretical gains in consistency or efficiency were not noticed. I have no way of measuring bolt thrust and can only guess at receiver vibrations by resultant accuracy. My rifle went from the dealer directly to the gunsmith, so base-line accuracy was not established with the standard chamber. The rifle averaged 1.53 MOA after the chamber improvement, so I assume that no particular gains were made in accuracy. The rifle was rebedded with Marine-Tex epoxy to no avail. Two known factors came into play that did not help in shooting tight groups. With the heavier payload, recoil at the bench was rather difficult to handle, and the fixed 4x scope developed parallax at least twice during load development. Recoil energy jumped up from 45 foot-pounds (ft-lbs) to 58 ft-lbs, and recoil velocity went from 17.8 fps to 20.3 fps. Compare that with a .416 Remington Magnum churning up 66 ft-lbs at 21.7 fps, and it’s easy to see that this was not a pleasant rifle to bench test.