I hope this tread isn't getting tired. I used my caliper and measured the two different blades ( the blade on my granddaddy barlow and the prototype GD barlow and they were the same thickness, 3mm at the blade stamp area of the blade. I used a 30 power loop and looked at the stamps. You can tell that the BUCK USA stamps were all done by the same machine. They all left a raised area at the bottom of the U in BUCK, and a flat edge on the top of the USA.
I did notice that the handle pins along with the spring pin, were all brass, on the Prototype and the spring pin and the bottom handle pin was SS on the other one. All in all its a nice addition to my collection and I am happy to have it.