My 2cents.
As H4831 already mentioned, a small 2.5x fixed is hard to beat. Leupold make a lightweight one in their FX-II series (4.9" eyerelief) as did Weaver not long ago.
Get a scope with lots of eye relief and mount it as far forward and as low as possible. I groove another cross slot with a dremel in an aluminum Weaver one piece base so the rear ring can be mounted forward (see pic with a Simmons 2.5x with 5"+ eyerelief). Get the base that extends out over the barrel. Weaver low rings are quite low. If enough eye relief permits, you don't need a hammer spur which I like alot (see pic). I find "see through" rings way too high.
http://www.leupold.com/hunting-and-...alight-riflescopes/fx-ii-2-5x20mm-ultralight/