Too close?

[DMS1]

One thing that no one mentioned (even me), is that shifting the scope away from your eye in the rings, it moves the bell farther down the taper of the barrel and creates a little more clearance. Even 1/8" can make a difference and not be noticeable...

I assume your somewhere in the transition of the barrel shank, hard to tell with the shim in the picture

 

[kamlooky]

Grinder, it's a flipp'in Remingtun.
Add sum karackturr tewwer.

 

[turbo_bird]

I'd make steel shims to go under both bases. Most aerosol cans are steel and somewhere around .008" to .010" thick. They make good shim stock once you sand the paint off.
Kristian