Here's where I'm ordering a .50 barrel in the next few days.
Notice they also have .311 blanks.
I don't have much interest in a .50 BMG. Bad shoulders & no place to realy wring one out. That blank will gather dust for a long time.
I have a LOT of learning to do on my lathe as I've never done any barrel work or anything else other than simple handyman stuff.
By time I learn some more machining skills, reamers may be available anyhow!
I'm not too concerned as it is such a simple chamber, with several ways to do it.
I just jump around from one project to another so much as I come up with ideas for each, that not much comes off the end of my assembly line! But I'm having fun & learning & gathering lots of new tooling, so It must be a GOOD THING.