Is the bottom one an 8x50R Lebel necked down to 6mm?
8 x 50R Lebel have been necked down to 5, 6, 6.5 and 7 mm
8x50R Lebel also necked to 7.5mm = 7.5x51R Berthau
Is the top cartridge (5mm) a new design or something necked down?
Were the necked down versions of 8x50R Lebel developments for use by the military or were they sporting cartridges, or were some military developments and some sporting rifle variations?
the ones I show are military experiments, not sporting ctges.
Check the date of the factory drawings (1891 and 1892) on the right
The two shown are unknown , meaning nobody I know has them in his collection