Yes, the 18.2 & 18.4 are metric bore sizes. These convert to 18.2 = 0.717" & 18.4 = 0.724". These would have been put on at the re-proof.
Note also on the original proof the in-between sizes, as the 14/1 were not used prior to 1887 so this gun should date to between 1887-1904.


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