For a scope with a 50mm objective lens, you will need high height rings.
MPN: VPR-30L would the the proper rings for your scope.
Yes, MPN: VPR-1H would be the best option for your scope.
The will depend on the specific model of Vortex Crossfire II that you have. Please email us at TechSales@OpticsPlanet.com with the size of your scopes objective lens and we'll be glad to recommend the appropiate height rings.
The ring height will depend on the scope being used. Please email us at TechSales@OpticsPlanet.com with the make and model of your scope and we will be glad to recommend a ring height.
Unfortunately, the Vortex Viper rings will not fit the CZ BRNO ZOM 451 receiver grooves because of the round receiver. These rings are designed to fit a standard Picatinny rail.
You could possibly get away with the lows as long as the rail on your Ruger American is at least .4" high off the top of the action.
You will definitely need the highs, but if you have a fixed, front sight on your AR you will require much taller rings then what are offered here.
Yes, you can use these rings as long as you purchase the appropriate diameter of ring for your Crossfire. Vortex offers over 10 different Vortex Crossfire models so the height and diameter will be solely dependent on the specific Crossfire model you have. If you can provide that information please feel free to email us at techsales@opticsplanet.com and we can provide a more specific recommendation.
Theres only a low or high set of rings that are 30mm, but the lows should work as long as the picatinny rail on your rifle is at least .4 inches above the top of the receiver.