I replaced my el cheapo crossbow scope with a Nikon scope and noticed the front bell of the scope is barely touching the receiver. Even though there's no recoil I'm wondering if I should put a spacer under the scope mounts. I suspect I should but wonder what everybody else thinks.

Did you up size to a 50mm from 40mm objective?

Just a thought but unless it's long range night hunting 50mm is not frequently needed and tends to bang into things. Even the 40mmscope do too but with rifle hunters those 50mm scopes are too big for most hunting.

If is a 40mm and you had a 40mm it should be the same gap or space. Just my opinion but I would have stuck to the 40mm objective.

In the other hand maybe you went from 30mm to 40mm, that's a good idea. Just get a taller set of rings then.

I found my old scope and it is a 4x32. The new Nikon scope is a 3X32 but the OD of the Nikon is slightly bigger. I replaced the old scope because it wouldn't hold zero. I suspect it was touching the receiver also. Time for higher mounts like you suggest. The 3X32 Nikon is much brighter/clearer than the old 4X32 scope.