Here's an alternative for a virgin hammer, radius the top of the extension to add some clearance, or file the entire top of the extension so it's not so high, you can also do the same thing on the bottom so it sits even lower, or if it hits the barrel release, mount it higher on the spur, lots of option. This one hit the scope before I took about .040" off the top and chamfered the top edge, also rounded the entire top edge of the spur on the extension so it's not so sharp.
Tim