You don't need a big front objective unless you are using a lot of X's. A 1-4X20 scope lets in EXACTLY the same amount of light when set on 4X as the 3-9X40 scope you bought when it is set on 8X. Move the 3-9X40 up to 9X and it lets in LESS light than a 1-4X20 on 4X or less. The advantage of larger front objectives is that it gives you the ability to use more magnification in low light. On a rifle meant for ranges inside 200 yards a 1-4X20 is more than enough scope.
