I just looked at a sq. butt model 10-6 with the heavy barrel. (Still "pinned").
It looked even larger in diameter than I thought. I don't have an example to compare.
I seem to recall a thread here some time back about the Model 10's original tapered barrel and the transition years to the heavy barrel models.
The point in that thread that seemed to stick in my mind about the heavy barrels was, there are actually two diameters of heavy barrels ??
Is that actual,...or one of my many memory tricks ?