Venom Visual Scopes

I would like to buy a red dot sight for my Smith & Wesson 22A-1 (7'' pistol barrel). The only information that I can find is that it is a 'tactical rail", but is it a "Weaver Rail", Picatinny, or some other type, and what size is the rail? I don't want to buy something and then have to modify the pistol in order to make it work. If someone already has a "red dot" on a 22a, the model and where you bought it would also be appreciated. Thanks.