Thankfully the rail system on my AR and Pistol was already installed and it is the picatinny rail system. After doing some research I found this was the most common industry wide and it is why most manufacturers are including picatinny rails as standard on their firearms. However I did come across another rail system that is just not as common but should be known of. 

Picatinny rails and Weaver rails are both mounting systems that are used to attach accessories such as scopes, sights, and bipods to firearms. The main difference between the two is the size and shape of the slots on the rail. Picatinny rails have evenly spaced slots that are 0.206 inches wide, while Weaver rails have unevenly spaced slots that are about 0.180 inches wide. Picatinny rails are more widely used and are the standard for many firearm manufacturers, while Weaver rails are used less frequently and may not be as widely available. Picatinny rails are generally considered to be more durable and easier to use due to their standardized design, but they can also be more expensive than Weaver rails.

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