Cupronickel fouling built up so thickly inside the bore some barrels eventually split from the pressure, so groove diameter
was deepened to 0.
I was under the impression that the barrel groove diameter
for these revolvers was right at .
Due to what appear to be intentional mismatches between bullet diameter and barrel groove diameter
, accuracy of the Model 1903 is not very exciting.
For this reason, the initial intension of wear evaluation by measuring the groove diameter
was changed to gravimetric evaluation.
The diameter measured to the outside of the blade determines the limit for the smallest possible diameter which can be machined, and the diameter measured to the inside of the blade determines the limit for the largest possible groove diameter
Trial groove diameter
is preset with an integral stop.
This weight, of course, is drilled out to a diameter that comfortably exceeds the groove diameter
of the barrel proper to allow passage of the bullet.
There seems to be no real standard for barrel groove diameter
with extremes such as these two barrels as well as chamber throats, which may be way undersized or way oversized.
The bore groove diameter
(the rifling's deepest point) for that caliber is .
The limitation depends on the insert and tool geometry, minimum groove diameter
, and problems with chip flow.
The advent of breechloading rifles permitted use of harder, longer bullets cast to groove diameter
400-inch groove diameter
and has always shot my home cast lead alloy 0.