The Mk18 ARCA rail is made for the long-range shooter, and unfortunately, is not produced very often. The design is actually quite brilliant. Put the ARCA Swiss quick-release system rail all along the bottom, with no need to add an adapter, and then M-LOK connection points at three positions on each side, and topped off with a full Picatinny top rail. This makes for the ability to slide a bipod or tripod with an ARCA adapter, or saddle, in the case of the tripod, the full length of the rail.
Because of its length and the need to support the rifle at various points along the rail with a tripod, the Mk18 rail is a bit heftier than other Geissele rails, and longer at 16", with the long-range shooter using an 18" to 24" barrel.
The ARCA rail is a limited production rail from Geisele. While it is a normal catalog item, it is produced on limited production runs. This is what might be called a classic, or new old stock, as the 16" rail has been retired from Geissele's offering.
The Mk18 ARCA M-LOK rail was adapted from the Mk16 rail, used by the US Military, and then morphing the lower section into a flat base for the ARCA style 35mm wide form with a 45 degree dovetail, that allows quick mounting to an Arca-Swiss Quick Release mounting base, sliding into any position along the rail. The MK18 features Geissele’s 2.25” long barrel nut that interfaces with the receiver and creates a platform that can be trusted to be straight and true the entire length of the free float rail. The 16” long MK18 is 3D precision machined using 7000 Series Aluminum to form a strong, rigid and lightweight profile.
The Mk18 ACRA rail is compatible with AR style rifles using forged milspec upper receivers for 5.56mm rifles
Note: Geissele is well known for changing the specifications on their rails, and not necessarily the SKUs. This rail is 16", and is 2023 production. The 2024 production rails are 16.5".
See review in Guns America Digest
Note: package contains rail, barrel nut and Allen wrenches. Does not contain gas block. Does not contain barrel nut wrench. If you have not purchased a Geissele rail before, you will need to add a Geissele barrel nut wrench
