On Sun, 29 Jan 2012 20:37:15 -0600, Louis Ohland
wrote:

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...
Greetings Louis,
Cobalt drill would be better but HSS will work too. As a bonus to the
hardness you will find that you can get an excellent finish on the
stuff using carbide. I would rather machine 4140 and 4340 in the heat
treated condition just because it looks so much better. And the nicer
finish also makes it easier to hold tighter tolerances.
Eric