Trapdoor ammo

[Merc]

I have a M1873 Trapdoor 45-70 and bought a McKeever ammo pouch a few years ago and gradually filled it with 20 Frankford 1880s cartridges from various gun shows in my area.

Most are plain brass cartridges but several cases are tin plated. Anyone know the reason they were plated?

[emmagee1917]

In mid-1888 a tin-plated brass cased, boxer primed cartridge became the standard. The tin plating inside the case was intended to increase the usable case life by slowing the galvanic reaction between the black powder and the brass case and preventing the the mercury fulminate in the primer from contacting the brass when fired. Tests later showed that the internal tinning lasted less than four years. The reason for the external tinning is simple - it's much easier to tin-plate an entire case than just a portion of it! Pattern 1888 production continued until 1898. Production for regular Army use ceased in 1895 but continued for reserve and militia use.
Chris

[Merc]

In mid-1888 a tin-plated brass cased, boxer primed cartridge became the standard. The tin plating inside the case was intended to increase the usable case life by slowing the galvanic reaction between the black powder and the brass case and preventing the the mercury fulminate in the primer from contacting the brass when fired. Tests later showed that the internal tinning lasted less than four years. The reason for the external tinning is simple - it's much easier to tin-plate an entire case than just a portion of it! Pattern 1888 production continued until 1898. Production for regular Army use ceased in 1895 but continued for reserve and militia use.
Chris

Thanks for the interesting expianation. I'll have to look at the dates when I return home - currently visiting a sister in Cave Creek, AZ.