MM SCOPE RAIL QUESTION GAMO WHISPER

[SGTMEATSAUCE]

I am thinking of dumping the sub-par scope on the Whisper and adding a red dot or halo/reflex sight. I have seen good reviews for the el cheapo Crosman for 10 bucks and seen China knock offs of EOTech type 552 for 100 bucks, and of course everything in between. For the price I like the A1-optical Halo/reflex, 40 bucks plus shipping. However most of the better scopes list "weaver" type rails or 22mm. What is the rail on the Whisper in mm? Any scope suggestions or ideas will be appreciated. I use the rifle mainly for plinking/target/small game in that order, most shots are 10 yards or so and as far as 40 yards max. 80% of my shots are 25 yards or less. Thanks!

[30-06]

I stand to be corrected, but i think all the gamos and most airrifles are 11mm. My Buddy Simon's scope rail is 11mm on his Gamo RSV.(Rsv and Whisper appear to be the same rifle?? Just another name maybe here in Suth Africa??

Can anybody tell me if there is a difference between the Gano RSV, Whisper and CSI??
JOHAN