Re: Glass for $400
There is a TON of info on this very question on this site. Let me help a little. Vortex, in your price range, you have the Midway exclusive Viper HS 5-15x44. It has a mil/mil setup (which, in my experience is easier than moa/mil). It has a Gen 1 mildot reticle which is adequate for most situations you'll be in with regards to paper/steel. I have one, it is a great scope, has nice positive turrets, it tracks well, the glass is clear...etc. At its price point ($400 on special, not sure if the special will apply to future orders, so it may be $500, which is MSRP) its got a lot of great features; not to mention the warranty which rivals, if not beats, the best in the business. The Viper line also includes other SFP scopes that has moa adjustments with a mil reticle. I've owned one and having matching reticle/adjustments is much more practical in my limited experience. Vortex listens to shooters and their wants. In my short time paying attention, they've released some pretty exciting products based on our communities communicated needs/wants. I know I am sounding like a fanboy, but so be it. They make a good product they stand behind. In this day and age, that is commendable.
Also at the price point you suggest, you have Falcon Menace scopes which are FFP (I'll leave it up to you to do your own research on the difference). I've been behind those scopes as well. They're okay. Glass is not stellar. The reticles aren't what I would like on an FFP scope, but they work. Warranty (which matters a lot to me) leaves me a bit mistified in that, to the best of my knowledge, the place you purchase the scope from handles all warranty interactions with Falcon. Again, not sure if that is the same as I remember, but when I owned a Falcon that is how it was. There are a couple other FFP mil/mil scopes, but I only have experience with the two above. Double your $400 and you get to another level (intermediate). Double that, you're starting to play with the big boys (lower end NightForce, some older used USO's, Leupold MK, Vortex Razor...which is a hell of a scope IMO etc). Double that, and you're buying the best (SB, USO, PH etc.).
That is how it goes in the world of glass. You've got a lot to learn...as I do. This is a good place to do it.