The comb height on some rifles is so high that low to medium rings may be too low for proper eye position. Take into consideration your size and comb height when selecting rings, mounts, and scope objective diameter. It is more important that it all fits for you, than what objective you have. Some 40mm objective scopes are just as bright as many 50mms even in the same brand. Size and weight can be important for some scope applications, and the 50mms are a bit heavier.