The Nikon Prostaff 5's with the 4.5-18x44 are great scopes but have 1" tubes, and they run about $350 "street" witha $459 MSRP but you can get them in mil dot, but with MOA turrets.
The Nikon Buckmasters are also available in 4.5-18 with a mildot reticle if you can find one its will be around $300 again mil reticle moa turrets 1" tube
The Millet 4-16x44/50 are good scopes they have mil reticles with the option of mil turrets, and from what I have seen using one of them and what ive read about them they are great scopes for the money. They do have a higher propensity for broken/bad scopes right out of the box but thats more of a quality control issue. they run about $300 but are 30 oz and 16" long a big scope
For around $400 you can get the Vortex Viper PA 6.5-20 in either 44 or 50 mm objectives both have a 30mm tube.
I looked at a ton of these scopes not too long ago I was in the same boat and When It came right down to It my $400 budget turned into a $550 scope but It was worth it, I got all of the features I wanted in a very well made scope. I went with the Vortex Viper HS-T 4-16x44 mil/mil scope and am glad I did. with all of the other ones I would be sacrificing something to save a little bit of money. Side focus Mil/Mil at least 16x magnification and a better than gen 1 mil based reticle were the options I wouldnt reconsider.
The Nikons gave me most of that except they use a standard mil dot.
The Millet gave me all of that but I wanted something lighter. a 30oz scope is alot of weight. And I also didnt want to spend that kind of money on a scope that is a decent optic to be sure but how long lasting would it be? and the reviews are either super positive or super negative. that concerned me.
Ive used one now and they are crisp clear optics with decently tactile adjustments, but its a very large and heavy scope that was almost comical on an AR-15.
After months of looking and saving some more I ended up going slightly over budget, the scope plus a set of Weaver 4 hole skeleton rings put me at just under $600 mounted.
And yes you can get a set of scope rings that you can switch between the AR and a hunting rifle, even with a standard gas block/front sight on the AR-15, with any sort of magnification you just blow right past it and dont see it at all. I have a Tasco 2.5-10 that I used on my Bushmaster 16" carbine for years and only on 2.5 power could you even sort of see that there was something there. On all other powers there was no "shadow" on the target or in the scope from the front sight. If you want a quick detach for the most repeatability get a Larue mount, and just put a spacer on the flat top of the AR for any clearance or cheekweld issues you may see.
Ive got my Vortex mounted on a set of weaver 4 hole skeleton x high rings and it sits pretty low, I could easily use a medium ring with 1/2" spacers to allow me to have the height on the AR that I need and the scope will still be low enough to swap to a hunting rifle.
Even with a set of super nice rings there will be point of impact shift swapping back and forth, but if you take note of your settings you should be very close to zero putting swapping it from gun to gun.
