I got a Tempil surface temperature marker that melts at 750 degrees F. The unit has a potentiometer to adjust the motor speed, so by regulating the speed of turn you control how long the brass stays in the flame. Mark a test case neck with the Tempil and time to when the paint/wax(?) melts. Then I up the speed just a few points so it is slightly less time (like from 65% to 67% - the scale is 0 to 99), so it is maybe 730 degrees. You don't want to see the pencil flame change colors, as that indicates you are burning off the alloy of the brass, so start short and work up into it. I also have a laser non-contact digital thermometer, but it's hard to get the brass and not the flame itself, so I recommend a Tempil pen over that.
