I am looking to get some opinions on a scope for my 7mm mag. It is primarily going to be used for hunting. And I am on a pretty tight budget. $500-600. I have looked at numerous scopes over the last couple of weeks. All this has done is confuse me. Some had adjustable objectives (which I don't really understand). I have used 3-9x40 scopes for the last 30 years. I would prefer a higher power scope for this rifle but, I am very hesitant to get one. Due to all of them having this adjustable objective. Some help would be greatly appreciated.
The adjustable objective gives you proper parallax adjustment for a given range. Parallax can be come a real issue at longer ranges and have serious effects on accuracy.
Non adjustable parallax scopes are generally set at the factory for 100-200yds.
If you've ever used an old style prismatic range finder you can understand how parallax adjustment can be of a great help at longer ranges.
As for what to buy.. .
In your price range you can probably go through the classifieds here at LRH and find a decent deal on a used Vortex or maybe even Leupold in something up to a 16x.
For most practical big game hunting 14x is enough to get the job done out to six or eight hundred yards, 16-20x really helps beyond that.
I picked up a used Leupold 4.5-14x Tactical with mil dot reticle and target turrets last year on Ebay for about 450.00 If I remember right, and something similar would work pretty well for you I'd imagine.
The Super Sniper's are also a fairly cheap way to go for some pretty good quality glass for a starter.
Personally I'd say when it comes to glass just save a little longer so you can buy the very best possible scope. You can spend a lot of money putting together a pretty nice rifle, loading ammo etc, and still not be able to hit a bull in the *** at 100yds if your scope is a POJ.
Some other decent scopes to look at used in that price rage would be Burris Tactical models, and the Bushnell Elite series.
If at all possible get a 30mm tube and 50mm objective as they will come in handy for low light shooting.
It really sucks to have a nice animal walk out just before daylight, or just before dark and not be able to see them well enough to "take the shot".
Don't be afraid to buy quality glass used especially from the better makers who give a lifetime warranty like Leupold, USO, and NF.