C4 MLOK Rail (12" Carbine FSP)

Usually Ships in 2 to 3 Business Days - Custom Cerakote Lead Times Vary (See Disclaimer Below)
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Centurion Arms LLC is happy to announce the C4 MLOK® rail.

C4 MLOK 12in FSP (For Carbine Gas FSB's)

The MLOK C4 rail system is based off the patented quad rail version. It is a lightweight, rugged, 2-piece free float rail that when installed gives the uppers a continuous 12o clock rail and MLOK slots for the 3,6, and 9 o clock positions. The C4 system is the lightest and most rigid rail that clamps to a standard barrel nut on all AR15, M4, and M16 type weapons systems. This design allows the installation of the rail on an upper assembly without removing the front sight post or permanently attached muzzle devices. **Some FSBs may need to be modified to fit by filing down the longer sling attachment ears so that they are not touching the handguard
Material: 6061 T6
Finish: type 3 hard coat anodized
Weight: 9.8 oz with screws --- 1.1oz more with standard barrel nut
Length: 12.565in
Height: Install 1.983 / end of rail 2.094
Inside diameter: 1.37
Rails: 1913 spec rail
Fasteners: grade 8 bolts with phosphate finish

***Please Note***

- Screws are included with the purchase of all rail systems and replacement screws are available to purchase if necessary

- Hex wrenches/keys are not included but installation will require 9/64" and 3/32" SAE Hex Keys

*** We recommend gunsmith installation for all of our parts.  We cannot warranty items damaged by improper installation.


Custom Cerakote Disclaimer:

Custom Cerakote is completed per order.  Our Cerakote room runs one color at a time so your ship date will be subject to the color rotaion at the time the order is placed.  You will receive an email confirmation once the item has actually been packaged to ship.

Cerakote items are not guaranteed to match separate batches or Cerakote completed by outside parties.  While we strive to keep our mix uniformed for our own products, we can't say for certain what Walter and Jesse cooked up in their lab out in Albuquerque.


  • 5
    Top notch as always

    Purchased this to upgrade my old basic Colt M4 and couldn't be happier. Once you clear the barrel of the Delta ring, stock plastic rail, sling slip and metal ring behind gas black this goes on like a glove. Excellent upgrade.

  • 5
    Looks sleek

    MLOK 12IN CUT OUT RAIL was as straight forward install. Great quality, finish and nice way to keep the front sight post and utilize the standard milspec barrel nut. Finish is close or is the same as my LE6920. Thanks Centurion.

  • 5
    Best Centurion Arms Rail yet!

    I installed a C4 MLOK FSB rail this weekend on an old Colt 6920 that had been relegated to the back of my safe. The lightweight nature of this rail, impeccable build quality, and flexibility afforded by the MLOK slots and extended FSB rail completely transformed my old carbine. I could not be more pleased. And as always, Centurion Arms customer service was second to none. This is the best Centurion Arms rail yet.