Kenny'
If the proofs show a chamber mark as in 12/C in a diamond then it was proofed after Dec 1887. If it does not have the chamber mark it would have been proofed prior to Dec 1887.

In either case, it would have the 13 denoting bore range at the time of proof. but after Dec 1887 the chamber size was designated.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra