Any decent bi-metal hole saw will work. But they won't last forever in 4130. Milwaukee, Lenox, Blu-Mol. Chinese stuff is useless. I use a variable speed 1/2 drill that maxes at 600 RPM. Speed and rate of feed is the trick, especially at angles that are not 90. If you are using too much pressure when the saw breaks through the wall of the tube, it will snag and clean the teeth off, especially when you get around to a 30 or 45 degree cut. Just let the saw cut, back off on the pressure, especially in the middle part of the cut where you're just in the thin tubing wall. A saw with 1 or 2 teeth off of it will still cut if you are using light pressure. Takes practice.

Sawzall instead of a chop saw? Milwaukee or Lenox, maybe 18 or 24 TPI. Buy several packs, they don't last forever in 4130.