jigman48
The gun shoulf be marked for both bore & choke. I am assuming the 18.0 (.709") & 17.3 (.681") are the choke dias for the two bbls. There should also be a bore dia mark such as 18.4 (.724"), 18.5 (.728") etc. Only with both marks can original choking be determined. Only by actual measurement can present choking be determined as it could have been modified over the yrs.

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