Rail systems on firearms are straight mounting brackets (usually made of strips of metal or polymer) on the gun's receiver, handguard or fore-end stock to allow sliding/variable-position attachment of Iron sights, Scopes , Holographic Sightsand other optical sights options. .Along with accessories such as tactical lights, laser sights, vertical/angled foregrips and/or bipods. Are examples of just a few options that may be used depending on a mission's need for the M4 is SOPMOD, amongst many other accessories like sling attachment points (which may be ether ring, loop and/or quick detach mounts using push button style hardware) to name just a few of the many options. An advantage with the multiple rail slots is the moveable positions to adjust for optimal placement of each item for each dif