Dialing scopes typically have LOTS of erector assembly movement. You can't get 120 MOA of movement in a 1" or 30mm tube. The specialty ELR scopes have 40mm tubes! The more room inside the scope, the more the scope can move. The parts (lots of them are in fact copper alloys) are bigger and heavier. ED glass is VERY dense, bigger internal lenses= heavy. Thicker, stronger main tubes to keep the scope with all its inherent weight from deforming... It's a product of being big and strong.
March has released a 5-42X56 FFP with 140MOA of elevation. It's 34mm tube has the same ID as a 30mm tube, it's the thickness of the tube wall (4mm versus regular 2mm) that accounts for the 34mm OD of the tube. The reason for the thicker wall is the scope is designed to be used, a lot, by all sorts of guns.
Also, the business about heavier glass and all, one needs to remember that in a variable riflescope, there's going to be a dozen or more glass elements and lenses and of those, only one or two will be ED glass.
My current March-X 5-50X56 has ED glass and a thick-wall 34mm tube and yet weighs a half pound less than my Nightforce NXS 12-42X56 which has a 30mm tube and does not have ED glass.
There's more to a scope's weight than glass and aluminum.
