Re: 40mm or 50mm objective
I have had three Leupold scopes (my three kids have them on the rifles I gave them) and two of them had 40mm objective lens and one had a 50mm, other than that they were identicle. The scope with the 50mm objective was clearer and brighter at all power settings. Shooting long range, which to me means over 600 yds, requires higher magnification, and high X requires more light to make it useable, and this means a bigger front lens to allow more light to reach your eye. I have a Varmint scope (6x-24x X 50mm) and when set on 24X there has to be bright sunlight because if it is a dreary overcast day the sight picture is very dim.