I don’t have a way to measure my bore diameter. I will say however I also have a similar era FWE 12 ga with 28” tubes with the left choke also measured 0.684”. That gun shoots 72% at 40 yards with that same Federal 1 1/4 oz #5 at 1330 fps.

Granted every gun is different and my sample size is insignificant, but it would appear that there is at least the possibility that LC was doing something different with their long range barrel.

I certainly wouldn’t expect ammo that’s probably 70-80 years old to perform as well as it did when it came off the assembly line.