I agree with Val.
One thing I would add is that some pistol scopes have parallax set for shorter distances (50 yards), as opposed to scout type scopes which are designed for rifle use and generally have parallax set for 100 yards. The Nikon Monarch 2X20 handgun scope is an exception (100 yards), there are some others. For optimal accuracy (consistency) you might want to consider a scope set more for rifle distances to minimze the effects of parallax. Since your goal is to shoot 4" groups at 200 yards, parallax is likely to be a significant factor. Leupold and Burris both make scout scopes, both are great - but they range in price $220-$260 (? haven't checked lately), more than many pistol scopes. If you have a pistol scope, it wouldn't hurt to try it out and see how well you do with it. If your cheek weld and stance is very consistent, it might work OK for you. If accuracy is real important and you want to spend some more, I believe the results will be better with a scope designed more for that use. Reticles might not be as thick - for better precision work, as well with the scout scopes.