I need to make up some .310 Cadet brass from .32-20 brass and one of the steps is thinning the rim. I know you cut from the front of the rim. Rather than having to re-index my lathe bit and measure for each one, I am hoping there is a faster way. Anybody have a way to do a quick and repeatable setup they can share?

No magic tool to use,sorry.
I just made a 100 cases using a small hobby lathe. I use a carbide bit and set a stop set to the correct thickness of the rim.
15 seconds per case.
Do you need any .310 Cadet or .32 Winchester Special barrels for your Martini?
I've been shooting and repairing .310 Cadet rifles for 55 years now.

Thanks for the reply. The barrel on my .310 is in excellent shape.

I have a take down action with the firing pin already bushed, along with .32-20 and .224 barrel blanks that will be fitted to it for a .218 Bee/.32-20 switch barrel.

Depends on your lathe.

You can set a stop as suggested, or you can read the numbers on your display if you have one.

You will be removing very little material, and for this sort of thing I just use my display.

Set it to zero at the finish, and that is it.