Thanks Drew.

Hatcher has a slightly different spec for 8620.

He claims, for WD 8620:

C .18% to .25%
Mn .70% to 1.00%
Ni .20% to .40%
Cr .20% to .40%
Mo .15% to .25%
S .07% max
P Not over .04%

I knew that that with the advent of smokeless powder rifle barrels had to be toughened up to resist erosion.

So, in 1931 Winchester couldn't just ring up Midvale or Crucible and say 'send us a car of 4135', right? That would have come maybe as much as a decade later?

"The price of good shotgunnery is constant practice" - Fred Kimble