Pressures are certainly a booga bo to be avoided in a double rifle, but another thing with rimless cartridges, in a double, is extraction, or the lack of extraction.

As far as pressures of the 375H&H, and the 416 Rigby,goes, the biggest problem is folks who are drawn to these type cartridges, have a habit of looking for MORE, and MORE velocity, and that even ups the already high pressures of those cartridges. Even with factory ammo both are high for the 18th century technology of a break top double. Ray is right, no matter if new or old, these cartridges are hard on doubles, and will shoot off face sooner or later. If you are a handloader, and have no experience with double rifles, sooner will be my guess!

Rays formula for pressure is not quite correct, but close. The tons listed for NE cartridges are in Imp long tons of 2240 lbs. The formula for his example is 14 LTs X 2240 = 31360 psi, not 28000 psi. Additionally,in defence of the old double rifle's stringth, the old standby 450NE 3 1/4" puts out 17 tons (17 LTs X 2240 = 38080 psi) with factory ammo. All this puts the Nitro proofed double rifle, of any quality, to be in the under 40,000 lb range, and most likely proofed with loads that developed around 45, to 48,000 psi. They would not take a steady diet of that load, however. The problem with the cartridges,416 Rigby, and 375 H&H, listed above they start out at much higher pressures in factory ammo.

The high pressures, when combined with the unreliability of a rimless cartridge, in a double, IMO, makes bad company!