1shotking, do this... take the bullet, load etc. that you wish to shoot, at the longest you wish to shoot, and look at it's trajectory at that longest distance in bullet drop inches and drop in MOA.

Then take the ACTUAL adjustment range of the sope you have and divide by 2 then add 20 to that for the 20 MOA base. Example 80 MOA as Thomae said= 40 up and 40 down(advertised) probable more like 30-35 up and down. So 35/2=17.5 + the 20 MOA base =37.5 IF the scope centers midway between the full adjustment top to bottom range which is rare on less expensive scopes.

If you find all of the above is true on your scope then it will reach close to 1000yds on the max come ups with maybe a 62gr(for the BC and wind) and zeroed for around 200yds.

So you shouldn't necessarily need a 20 MOA rail. I have the Bushnell on a tactical rig and it didn't have enough elevation knob adjustment to use the 20 MOA.

Hope this helps you decide.