I've always done my own, w/o any machine tools like a lathe, etc, and with very decent accuracy resulting (40 years) - here's how:
I use a solid bench vise, w/padded jaws, to hold my work steady.
Use a tubing cutter to mark the bbl for your hacksaw cut, and a small machinist's square (borrowed is OK) to ensure your cut stays square (to the bore).
Carefully file the cut end smooth, taking care to keep the end square, then break the inside edge of the bore with a chamfer bit (held in a hand/power drill will work).
I also break the sharp outer edge of the bbl/muzzle - but YMMV.
Get a small can of fine/coarse valve grinding compound from an auto parts store or automotive machine shop, and buy a selection of various sized brass round-head screws to use as crowning tools (hardware store).
Plug the bore & chuck an appropriately-sized screw into your drill, before dipping the screw head into the coarse compound.
Rus the coarse compound loaded brass screw head against the muzzle/bore while running the drill & twisting it about at various angles.
Switch screw head sizes to address a different section of the crown, until there's a smooth transition at the end of the rifling.
Then, do it all over again, but with the fine compound.
Flush all the compound out between grits, and after you're done, then push out the plug from the chamber end.