So I have a Gracey trimmer for 223 but it was substantially less buying without the motor, and when I started doing 300BO I bought one of the WFT trimmers. At first I used a drill press and that worked pretty well (had to rig up something so the base of the Gracey didn't rotate) but it was fatiguing to push the case up (ETA: My wrist works better when it is not upside down) and hold it at the same time, and if you lost your grip on the case it fell, or if you wanted to reposition your fingers you had to pull it out and start over.
So I figured there should be a way to make gravity my friend, and I went and bought a cheap drill at Walmart. I ended up with this one (that might be discontinued) just by buying the cheapest thing they had at the time, but there were two critical features that I figured out just by a happy accident. Even though it didn't come with a handle, it had the cylindrical area at the front where a handle would clamp on, and as it turns out, a 1-1/2" muffler clamp from he car parts section. And it also has a variable speed knob that adjust the RPM WHILE IT IS LOCKED ON. A couple of coupler nuts and it bolted right up and I mounted the board under the bench. While the drill I used doesn't seem to be available anymore this one is only a few bucks more. Or you might already have a drill with a handle.
Anyway, worked out sweet enough I thought I would post. This even makes two handed operation great, you can drop it in with one had, and then grab it with the other hand for the cutting, while hand number one goes back and finds and orients the next case. When one hand get tired you can swap the bins around to switch hands.