Rifle scopes come in 3 basic tube sizes.
1", 30MM, and 34MM.
1". Pros: extremely common and available at any store that sells guns/sporting goods.
Every scope manufacturer makes a decent 1" tube scope.
You will be able to find rings for this scope almost anywhere.
1" Cons: The smallest of the tube sizes allows for the least amount of light transfer to the shooters eye.
The small tube size makes the amount of internal adjustments much less than the other larger diameter scopes, limiting the distance you can dial your scope up to without using holdover.
30MM, Still extremely affordable with manufacturers making models from the low end all the way up to the highest of their product lines, makes scopes with this tube diameter one the most popular, if not the most, of all scopes.
Since there are so many of these scopes, with a variety of features, the shooter can get a scope with every option they are looking for at the price point they are willing to spend.
The bigger tube allows for more light transfer as well as more internal adjustability for longer range shots without using holdover.
30MM Cons: Though these are common, sometimes finding rings is not as easy as their 1" tube cousins.
34MM Pros: These scopes are almost always a manufactures top tier product line offering the best light transfer, adjustability, and clarity.
You just cannot go wrong with a 34MM scope made by a reputable manufactured.
34MM Cons: Since these scopes tend to be on the higher to highest product line, they fetch a good price.
Finding rings can be a problem at some if not most point of sale outlets, so finding one you can take home with you without waiting can be a problem.
It's just common since, the bigger the objective lens the better, more light transfer, more field of view and on and on.
However the is a negative to the bigger lens. The larger your objective lens is, the farther away you need to mount it from your action, using taller and taller rings.
As you push the scope up and away from the action you also make your head, and most importantly, your stockweld, comes off your stock. Many shooters do not take the time to rebuild their stockweld back up in order to get the proper eye relief along with a good stockweld.
Parallax defined, is the internal adjustment of the scope, placing the object you are looking at (Objective) on the same focal plane as the reticle.
Since the best way to check to see if you have Parallax, which looks as if your reticle is floating around your target, is while you are on your rifle looking through your scope, it is our opinion that the best scopes for shooting distances are those that have adjustable Parallax and that the adjustment is on the side of the scope.
First thing is this, NEVER get a scope that has adjustment in INCHES, They just do not work. In shooting long distances EVERYTHING is done with angles and in this genre the two just don't work well together.
M.O.A. or Minutes of Angle is just a smaller breakdown of 1 degree. 1 degree has 60 MOA. This unit is measurement is easiest to learn, as it almost translate to a 1-1 with yardage. 1 MOA at 100 yards is about 1", 1 MOA at 200 yards is 2" and so on.
MRAD, or Mil Radiant is just another break down of a circle. Instead of degrees the circle is broken down into RADIANS with sub-measurements in those Radians being in tenths in most scopes that come in this flavor.
This unit of measurement is a bit more difficult to learn (But not by much) but since these units of measurement are divided into smaller sections of a circle, they allow much more accuracy matching them to the ballistics of your weapons system.
This really comes down to personal preference, but we will point some things out.
We highly recommend getting a scope that has some sort of sub-tensions and not a scope that just has a basic reticle (Just the vertical and horizontal crosshairs converging in the middle) .
Sub-Tensions are the "Hash" marks that go along the crosshairs. These also come in a wide variety of options and measurements.
Whatever scope you get we also suggest getting your Sub-Tensions in units of measurements (M.O.A., or MRAD) that match your turrets. Having one with the other often leads to too much math being done in the field and a headache on your way home from the range.
This too, is mostly personal preference. Obviously the farther out we want to shoot requires us to actually be able to see what we are aiming at, thus requiring higher and higher magnification.
At our facility we recommend a scope with at least 12 power magnification.
Whatever scope you get just make sure the scope does not become blurry on higher magnifications as some lower end scope tend to do.
We also leave this to the individual shooter.
For those who do not understand or know what this is or means, we will help clarify it.
As the image, or objective, transfers through the prism inside your scope it is focused on several different "Planes", But not to be mistaken with Parallax,
With a FFP scope, as a shooter zooms in and out of magnification the reticle and objective zoom in and out on the same focal plane. What this means to the shooter is that whatever units of measurement their sub-tensions are in remain constant and are a "Valid" unit of measurement throughout the magnification range.
With a SFP scope this is not the case. The object and reticle are focused on two separate focal planes. So, when the shooter zooms in and out of magnification the sub-tensions do not remain accurate. Most, it not all, SFP scopes only have their sub-tensions valid and accurate at full magnification.
When it comes to the scope turrets we suggest this.
Whatever scope you decide on it should have adjustable Elevation and Windage Turrets that have some sort of mechanism to "Disengage" from the internal mechanism of the scope and rotated back to where the "0" or zero mark lines up with the witness mark on the scope body, and then reengaged.
Manufactures have a wide variety of how they achieve this, some have set screw you loosen on the turret, others you simply pull up, and so on.
Some manufactures however are still using a "Modified" friction plate design. You all know this type of "Turret", you know the ones we used to put a coin in to turn the adjustment's.
Some manufactures have modified these style of turrets to look somewhat like the style you should be using, but they offer no way to disengage the turret from the mechanics of the scope to reset them back to the "0". This makes it extremely difficult to remember where your zero is. So check this out before you buy, these style of scopes usually have this style of turret on the windage side of the scope.