Anyone ever cut a shotgun chamber using a boring bar? What could go wrong? (24ga, can't find reamer).

1. Yes.
2. It wasn't very smooth and required honing. I used too sharp a tool bit in the boring bar. A rounded carbide one would be better but that was back when I was stupid.
I would consider making a reamer; even a half moon one.

I too suggested a half reamer .. as the 577 is about as simple a chamber drawing as can be imagined, would make sense to try

if you DO you a half reamer, you MUST rough the chamber first .. run in a drill to remove what you can before chambering

https://www.practicalmachinist...amber-reamer-313922/

I did a test barrel stub to find the angle for the compound (about 1 deg) and that seemed to come out OK. Used a chucking reamer to get close to final dimension. So I made two tubes for sleeving, pretty straightforward, just took my time and used a sized and bulleted dummy round for a gauge. Made a cutter that cut smooth and left a 45 degree step at the end of the chamber. Did not need a throat as these are smoothbore barrels. Now for the chokes ... it's going to be a paradox with permanent choke tubes. Had a ML guy make me up a piece of barrel with the right alloy, twist, deep grooves .. got Manson working on the choke tube recess reamer. Then finally the monobloc, that's the trickiest part but I have done that before.