< 1/4" "stepped" forcing cones were designed for brass 12A (NOT 12B which indicated bore size brass hull) and early paper hulls
http://www.parkerguns.org/pages/faq/12B.htm
I don't know when the 1/2" cone became standard.
The stepped cones and bore size of Parker Lifters has been discussed on the PGCA Forum
http://parkerguns.org/forums/showthread.php?t=22332
http://parkerguns.org/forums/showthread.php?t=5891
- 70,000 SN would be c. 1891. That would seem to be very late as the Brown designed Smith hammer (1894) and hammerless (1886) had 1/2 forcing cones and 2 3/4" chambers

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