Don't have any info on J T Powell. The 14 means that when the gun was proofed the bores would accept a 14 gauge plug Gage (.693") but not a 13 gauge one (.710"). It was proofed prior to the chamber size in diamond marking. I have a Birmingham proofed W Richards which also has bores marked 14 but has 12 gauge chambers. It was either built with undersized bores or has been subsequently rechambered. I am betting it was built this way.

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