Lessons I learned reaming my first chamber today;
-Use sharp reamers!
-Don't use much pressure to advance the cut after initially biting into the barrel (depending on the leade cut, some force may be required to get the first chips going when you start out)
-Since flutes will try to catch on the rifling lands, pre-drilling the first bit of the bore to eliminate them (or get closer to the finish diameter) will make holding the handle/wrench steady during engagement much easier & safer (lathes are powerful, and you are basically resisting several times the torque of a twist drill for reaming, minimum; if it catches you could get hurt if you don't position your grasp on the wrench strategically)
-Clear chips frequently & inspect for flute damage when cleaning them out
-The reamer will stabilize after the first 1/4" or so of cut, and begin cutting more quickly with less force. Be aware of the change so you don't let chips build up too quickly or overshoot your mark
-In my case (HK33 barrel) it was easiest to headspace by chambering past where I needed, and facing the barrel back to proper case protrusion. Easier to dial in a lathe apron than a reamer depth (due to spring back and 'grabbing' of the walls during reaming, it can be difficult to get the depth right to the thousandth in accuracy, especially since cutting too slowly causes chatter)
-Even O1 drill rod homebrew reamers (45acp) can be run faster than you think without being damaged, and actually cut better, but remember that bit about having to control the wrench while doing so
-You will likely (almost certainly) need to polish the chamber with an abrasive flap or small stone after reaming (you can end with small burs at the neck/shoulder transitions, as well as the sucky-but-often-inevitable scoring from a chip that gets by the flutes during cutting)
Reamers are just fancy drill bits (not even that fancy, or they'd be spiraled
) so they
will cut what you need, and for many barrels, also. But they are also very expensive or a real chore to make, so anything you can do to reduce their workload is worth it. That's what pre-drilling and roughing reamers are for. Roughers can have tougher cutting surfaces, and leave a reduced profile that is strategically shaped to support the finish reamer nicely for the followup and prevent chatter & reduce cutting forces.
Speaking of 50BMG barrels; it pays to know if your barrel is chrome-lined or stellite-lined
before ruining a reamer on it (not my lesson, but a friend's
)