If you have purchased an AR-15 within the past few years you might have noticed the lack of a carrying handle. Older models of the AR-15 used to be equipped with handles making it easier for a person to carry, the handle made it as though you were simply carrying a briefcase.
However, earlier models of the M-16, AR-15 platform, had started to put scopes on top of the carrying handle. Though this was phased out in the 2000s, due to recent advances in optical systems. For example, three scopes, or optical systems, that come to mind would be government contract models such as: Aimpoint, Trijicon(ACOG), and EOTech.
The main problem with attaching a scope to a carrying handle is the dilemma with visibility, eye relief, and grounding the scope onto a rear sight post.
Since the retirement of carrying handles, scopes and optical systems have now been directly mounted onto selective integrated rail systems, also known as Picatinny Rail Systems. This aided in Marines and Soldiers having better eye relief from looking through scopes for extended periods of time. Grounding of the scope onto the rear sight posts is incredibly important for accuracy while aiming and shooting. It also aids in zeroing your AR-15 on the range.
All three scopes: Aimpoint,Trijicon (ACOG), and EOTech, are all screw in systems which are easily mounted to the S.I.R. (Selective Integrated Rail) System. All three of these recommended optic systems are used by the United States Military, and the mounting is tool-free, aiding to the ease of attachment.
If you happen to own one of the older models of the AR-15, such as the A-1 or A-2 models, unfortunately the carrying handles are not removable.It was not until the creation of the A-2 prototypes and A-3 models that the carrying handles became removable, in an effort to mount optics and scopes directly to the rail system. So mounting a scope onto one of these older models will be a little more difficult, and you only have one option. You would have to mount the scope directly to the carrying handle.
Doing so, unfortunately, is very cumbersome and your accuracy decreases due to the lack of grounding with rear sights. Also, adding to the fact that it will make the overall weight of your weapon more as well.
If you do not have a detachable carrying handle, you do need an adapter to allow for mounting of your chosen scope or optic system to the handle of your AR-15.
Attaching your chosen optic system or scope to your AR-15 directly grounded to your rail mount also allows you to mount a flip up iron sight in front of your scope. Should your optic system go down for any reason, you will have back up flip up iron sights. These iron sights are very useful to any operator in the field, or devoted gun enthusiast.