Mounting a scope on an AR15
Posted by Andre on 1/10/2012
We get a lot of questions at gun shows and one of the most common is this:“I just got a new AR15. How do I put a scope on it?”
This is a great question and there could be many answers. I almost always have to answer their question with another:
“Is it a flat-top or a carry handle?”
Truth be told I’m always hoping they tell me that it is a flat-top. It just makes mounting a scope so much easier. With a flat-top you can just use a good set of medium to high rise Weaver or Picatinny scope rings. A flat top AR15 will accept both. Or there is a multitude of one piece scope mounts that are designed specifically for flat-top uppers. When they tell me that it’s a carry handle then things get a little more involved. It isn’t difficult to do by any means but it does require additional considerations.
But then I usually have to ask the question:
“What kind of scope do you want to put on it?”
Most people in the North Dakota/South Dakota region (where we are located) only use their AR15 for varmint hunting and plinking. This means that they almost always want to install something in the 3x-12x variable magnification range, with the occasional fixed 4 power scope. Very few of which have an objective lens greater than 50mm. So I will talk about these scopes and the related mounting options. I realize that there are 1000s of other kinds of scopes out there but for the sake of simplicity I’ll focus on these.
First you need to know the objective lens diameter of your scope or the scope you want to put on it. The objective lens diameter is the size of the “bell” that faces the target. It is important to know this number when mounting a scope on any rifle to make sure you will have enough clearance above the barrel or receiver of the rifle. All scopes will identify this information in the manufacturer description or title. Most people see it without ever realizing what it means. It is the last number after the magnification range used when describing a scope. An example would be 3-9x40. This means that the scope would have a magnification range of 3x – 9x and that it has an objective diameter of 40mm. Likewise a scope described as 4x30 will have a fixed magnification of 4x power and have an objective diameter of 30mm. The same is true for almost every scope. It is also important to know the tube diameter of your chosen scope. It will either be 1” or 30mm. This information can be found in the product description of the scope or it will be in the user’s manual. That being said, let’s look at the AR15 mounting options.
First I’ll talk about the easy one;
Mounting a scope on a flat-top AR15 – Scope rings
This is by far the easiest and cheapest way to mount a scope to an AR15. Like was stated previously you could just use a good quality set of medium to high rise scope rings depending on the scope. Most people will choose to use high rise rings for a more comfortable cheek weld. Some others will actually need to use scope risers in addition to high rise rings to accommodate their shooting style. All of this can be had for as little as $10-$15.
Mounting a scope on a flat-top AR15 – One-Piece Scope Mounts
Now here is where some of the more involved options start to show up. This is going to be a lot more stable when compared to rings alone. The reason for this is that there are less individual parts between the scope and the receiver. This is usually my preferred method. Generally speaking most one piece scope mounts will be able to accommodate objective diameters up to 50mm. some good examples of these are:
One concern with these types of mounts is the amount of eye relief that they will allow. Keep that in mind when choosing your scope.
Carry Handles
There are those that want to keep the functionality of iron sights while at the same time having a magnified optic. For these people mounting a scope on the carry handle is usually preferred. If they have a flat-top AR15 than they will need to first purchase a detachable carry handle and then a carry handle scope mount of some type. If they already have a fixed carry handle on their AR15 than they will only need the mount. The two main styles of these are the rail and the integrated ring mounts. Some examples:
The biggest thing to keep in mind when mounting a scope to the carry handle is the fact that it raises the scope to well 
above the bore of the rifle and as such may require some type of cheek riser to be able to shoot comfortably.
Well I hope that this has been informative for any looking to mount a scope to their AR15. Until next time.
