Parker gauge determination

[Jack Hamner]

Question--I just took my old Parker hammer gun to a well known sporting goods chain to see if I could find out the gauge of it. It was sold to me as a 14 gauge and I was curious to see if this was true. The man at the store, a 27 year veteran, tried to insert a 12 gauge measuring device into the chamber but it wouldn't go in. He then inserted a 16 gauge device into the chamber and it wobbled around with with a moderate amount of "play". From this, he concluded that the gauge was between a 16 and a 12, and probably a 14.
I read somewhere that to ascertain the true gauge of a shotgun, you had to insert a caliper device into the barrel and take a measurement at it's widest point and go with that measurement to determine gauge.
Someone did this for me a while back and determined that the gun is a 12b gauge.
Now I am TOTALLY confused! Which method is right? I would love for the 14 gauge determination to be correct and I feel that it is a possibility--the gun is early--serial number is in the 900's and barrels are decarbonized steel.
Any thoughts on this? Thanks!