McGowen barrels are good ones.
Their .458-caliber barrel had a true minimum groove diameter of 0.458" last one I bought from them.
The Pac-Nor was too.
The factory CZ barrels I have slugged are 0.459" like on most .458 WinMag factory rifles, Winchester and Ruger.
SAAMI minimum spec is 0.458" for barrel groove, and maximum bullet spec is 0.459" diameter.
I think my Shilen barrels are about 0.4585" so rounds up to 0.459".

I heard the McGowen factory is making the inside steel tube of carbon-fiber wrapped rifle barrels
for some brand nowadays too.

Ron aka "Rip" for Riflecrank Internationale Permanente
NRA Life Benefactor and Beneficiary
.458 Winchester Magnum, Magnanimous in Victory
THE WALKING DEAD does so remind me of Democrap voters. Donkeypox.