The attached picture shows 3 x 50 Browning rounds. The right hand cartridge is the normal 50 Browning H/S FA 20, the left hand round is H/S W 19 and is (I think) the Winchester experimental round shown at Fig 329 in the History of US SAA (revised) . The round in the centre has no H/S and is marked as model M1919 but the dimensions are not correct for this. It has the same dimensions as the Winchester experimental (rim .740, head .750, neck .546) except that the case is 4.07 inches long. In the History of US SAA there is reference to a rimmed cartridge this long which was then converted to a rimless case. This was later shortened to 4.02-4.03.
Can anyone provide any information on the centre cartridge?