I have developed an M1 Carbine using a.25 cal cartridge using a necked down .30 Carbine. Nothing spectacular, just something to do on the week ends. Redding made the dies from fire formed cases. Now I need to know how to accurately measure the shallow shoulder angle. Math was not my best subject. I don't have a tool small enough to fit. Any suggestions?

Try taking a photo of the case and blowing it up. Then use a protractor on it to measure angle.

Why not ask Redding or the reamer maker?

To Maz and Curley. Thanks. Never thought of the photo. Have question into Redding. No response yet.

Measure length of case, subtract length of neck and length of body, then you know length of shoulder.
Measure dia of neck, and dia of body at shoulder.
Draw a right angle, and marke it with .001" increments up and sideways, and plot out the length upwards and dia difference sideways.
There's your angle, as read from a protractor.