templates?
templates???
we don' neeed no steenkin' templates!
vernier you magazine...add .010" to that. let's call that 'x'.
vernier you current mag opening. let's call that 'y'.
subract y from x and divide by 2.
this is the amount to remove from each side of the magazine opening. scribe that line with a nail and a straightedge.
file to those lines.
go slowly and keep checking for fit with your magazine as you go.