sw282:  All my rat rifles wear the same scope, the Leupy VX3 6.5-20X 40mm LR with VHR.  So far after many years of launching grass rats, this model has worked out perfectly.  Low power for scanning, plenty of power for those little 'peekers' over their mound at 400 yards.  And the wind hold-off ticks are especially nice in the reticle.
 
By going with the 40mm model, the scope can be mounted very low over the bore to minimize any effects of canting.  With a bubble level, the effect is then zero.  Also no need for a hulking 50mm objective unless you hunt a lot at twilight or dusk.  From experience, PD's and ground squirrels do not come out then anyway.  Lots of opinions on this one, but this is what has worked for me on all my primary rat rifles.  I think there's nine of them now in the safe. 
