Installation of the AR MREX Rail System
Difficulty: 6.5 / 10
This installation seems more complicated than it truly is. Timing can be repetitive but take your time working through each step and you will have no problems.
These instructions are for the AR-MREX installation, please follow gas block and muzzle device installation instructions separately.
Required tools:
● KDG Custom Barrel Nut Wrench (included)
● 1/8 Hex Driver
● Rem Oil or equivalent grease
● Upper Receiver Action Block
● Vice
● Barrel (w/ low profile gas block)
● AR15 Armorers Wrench
● Torque Wrench
● Red loctite or equivalent
Prepare the rifle:
Please be sure your firearm is unloaded and there is no ammo near your workspace.
Split the upper and lower receivers. Remove the BCG and charging handle and set aside. Set the lower receiver aside, it will not be needed during installation
Prior to installation of the AR-MREX, the barrel assembly will have to be disassembled. We also recommend removing optics and other accessories from the firearm.
Timing the AR-MREX Barrel Nut:
The AR-MREX Barrel Nut has threads on each side, this will allow you to use the minimum amount of shims. Always use as few shims as possible .There are three size shims in each kit (Orange .001 / Green .005 / Blue .010)
1. Place the barrel into the upper receiver barrel boss.
2. Apply a small amount of oil to barrel nut threads on the upper receiver to protect the treads during installation and allow for proper torque.
3. Add and remove shims between the barrel nut and barrel until you are able to find the correct combination needed for your receiver. (Note: the barrel nut is two sided with opposing threads to aid in timing)
4. With shims and barrel installed, tighten the barrel nut past 35ft/lb but never exceeding 65ft/lb until timed. ***Repeat steps 3 & 4 until the an appropriate amount of shims is found to meet the torque spec range*** ***DO NOT add shims between the barrel and the receiver! The barrel nut is properly timed when the gas tube hole in the barrel nut is aligned with the gas tube hole in front of the upper receiver and the barrel nut is between 35-65 ft/lbs torque.
5. Install low-profile gas block onto barrel assembly using the barrel manufacturer’s or gas block manufacturer’s installation recommendations.
6. Install muzzle device using manufacturer recommended installation.
7. Slide the AR-MREX completely down the barrel assembly, onto the properly installed barrel nut.
8. Apply loctite to each of the 6 rail fasteners. Install and torque to 45in/lb using a criss-cross pattern.
Congratulations, you have successfully installed the AR-MREX
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