Military Cartridge Section
.50 Remington Army (M71)
The .50 Remington a/k/a .50 Remington Army (M71) cartridge  was the second version of this caliber.
The first version: .50 Remington Navy (M67) was introduced in the U.S.A., around 1866 for the Navy Model 1867 (M67)
rolling block pistol
and was a straight, with very slight taper, rim-fired cartridge and later as a straight walled center-fire case.
The later version (below) .50 Remington (M71) Army was a “bottle necked” case for the Remington Army Model
1871 rolling block pistol
introduced in 1870 had an “Inside Primed” Benet Cup internal primed center-fired cartridge.
Then later, sometime around 1873, the cartridge primer changed to an external primed (Martin Primed) and later to a regular, more
modern, outside primed case.   
Ammunition was loaded by both Remington and Winchester and was available until about 1920, making this caliber obsolete for
over 96 years on regular primed and up to 146 years on inside primed at this writing.
The Army (M71) version has a large diameter projectile and will not fire in the
Navy (M67) rolling block pistol.
Below .50 Remington (M-71) Army Rolling Block Cartridge
Benet Inside Primed
.50 Remington (M71) Army
rolling block cartridge
produced by Frankford
Arsenal, 1872 production.
(145 years old)
Internal "Benet Cup"
experimental primer only
made for 2 years before
changing to  a "Martin
external primer".
Note the 2 machined crimps
outside the case that hold
the internal primer in place