Folks, I'm looking at boring a 5/8 inch diameter by 5 inch long hole
through 4140 PH, so I can make a barrel stub for my TC Contender.

From initial comments, I'll need carbide to do this... BUT... pure
carbide needs rigid setup, which I don't believe my Grizzly G9972Z lathe
has. Once I punch through a 1/2" hole, then I can whip out my CCMT
boring bar and do it.

Will HSS or cobalt drills get er done?

Heat treating would add more cost to this than it's worth. Really, if I
could find a clapped-out Contender barrel, I'd saw the barrel off, bore
it, and stub it. But barrels are not cheap on ebuy...