I posted a thread years ago that will figure it out, as long as you know some measurements. However, unless that chassis has an extended flat top receiver, like an AR, either of those ring heights will be more than enough for a 56 objective. Here is copied text from the post:
[rail height + ring height] - [bell diameter x 0.5]
If the value is positive, then your bell will clear the barrel. Ideally, you want that bell to be about 1/4" or less over the barrel. This will give you a tight cheek weld. Be sure to account for Butler Creek caps if you intend on using them.
If you are using a 40mm objective, then you can use the lowest rings and bases available, as the bell will certainly clear the barrel with no problem. i.e. don't worry if the bell ends up being higher than 1/4" over the barrel.
Just another note. If you are using a scope base and/or mount/rings that have built in elevation, that may have to be accounted for in the case of very small clearance. To calculate this, we need to know the amount of elevation built into the mount/rings and/ or base, and the length from the end of the scope base to the end of the scope bell. Convert MOA into degrees, and then the equation is:
Tan ? x length
For example, if you are using a 20 MOA base, and the distance from the edge of the scope base to the end of the bell is 5". 20 MOA = 0.333 degrees, so:
Tan 0.333 x 5 = 0.029"
This means that you need an extra 0.029" of clearance in addition to the calculation above
