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Nitro –Why settle on the .577 x 23/4 inch case, thus putting yourself in a straight jacket pressure-wise because of it’s lower powder capacity?

Since Bertram Brass sells 31/4 inch cases, why not go a step further than 3 inches, and utilize the extra case capacity to further minimise pressure if there is a concern about action strength. Alternatively, if the Greener action will handle it, the longer case may allow use of the more effective 750 grain pill and/or higher velocities than is possible out of the 23/4 inch case?

The 31/4 inch case length was used in both Black Powder and Full Nitro loads, but became obsolete very early on; the Nitro round loosing out to the 3 inch, perhaps because the rifles of the day were “built from the ground up” to handle it?

The Black Powder round was quite a rare – examples are harder to find than rifles chambered for it. I once had a Jeffery boxlock in this chambering (to this day I regret selling it!), and I have seen two others, a boxlock and a Jones underlever hammer gun – also Jeffery’s! Perhaps this cartridge was a Jeffery development? If so, this would be counter to Wal Winfer’s theory that .577 was one bore size that Jeffery didn’t work on (see British Single Shot Rifles, Vol 3, pp 213). All three guns had Black Powder proof markings, but before 1925 when Nitro Proof became mandatory, it was not unknown for guns built to “full nitro” proportions to carry Black Powder proof marks. Curiously, none of these Jeffery’s regulated with 650 grain pills, but all shot with 750 grainers, perhaps adding further weight to the possibility that they were in fact, Nitro rifles?

I developed duplex nitro/black loads with 750 grain lubed cast lead projectiles for my rifle that came close to duplicating the ballistics of the “full nitro” .577 x 3 in round, with very acceptable pressures. Jacketed pills would give even lower pressures, as would full nitro loads.

Another avenue to achieving better .577 calibre ballistics via larger case capacity might be the 577 Rewa – essentially a necked down 600 Nitro. This round was designed by Holland & Holland in the late 1920’s for the Maharaja of Rewa, who was disappointed with the performance of the 600 Nitro, and wanted the improved penetration of the .577 projectile.

When building a .577 double rifle on a 12 bore action, available chamber wall thickness (dictated by standing breech dimensions) would determine which case type would be appropriate. Personally, if this was my project, I would get hold of one of the Spanish Zabala 10 bore shotguns, and work with that!

Remember, you always have the option of easing back on the throttle if you want lighter loads for range practice or lighter game!

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