7 Super mag is a 357 Max case necked down
I had a TC barrel in it
I bet you need to nose size , I have to for several rifles with tight throats
I had to get a custom sizing die
You size the bullet nose first , but stop before the driving bands , with just a little spray on case sizing lube
I had a freind make it
Or you can have a Gunsmith lengthen the throat till the bullet you want to use just fits
Johnch