Upper Receiver Assembly (AR-9, AR-15, and AR-10/LR108)
Step U6: Muzzle Device Installation
Objective: In Step U6 of upper receiver assembly, we will install the muzzle device.
Tools Required
1: Refer to the manufacturer’s instructions and specifications for your muzzle device for the size and type needed. Some muzzle devices come with the required wrench (e.g. VG6 Epsilon, Precision Armament HYPERTAP).
2: The table below includes the appropriate wrench for our recommended muzzle devices:
| Device | Installation | Type/Flat Span | Recommended Tool |
|---|---|---|---|
| A2 Flash Hider 5.56mm | Crush Washer | 0.750″ | 3/4″ Wrench |
| A2 Flash Hider 7.62mm | Crush Washer | 0.750″ | 3/4″ Wrench |
| Noveske KX3 5.56mm | Crush Washer | 0.750″ | 3/4″ Wrench |
| Precision Armament EFAB 5.56mm | Timing Shims + 20-30 ft.lbs. | 0.750″ | 3/4″ Wrench |
| Precision Armament EFAB 7.62mm | Timing Shims + 20-30 ft.lbs. | 0.750″ | 3/4″ Wrench |
| Precision Armament Hypertap 5.56mm | Timing Nut + 20 ft. lbs. | Spanner or 0.828″ | Included (no torque) or Adjustable Crowfoot Wrench |
| Precision Armament Hypertap 6.5mm | Timing Nut + 20 ft. lbs. | Spanner | Included (no torque) or Adjustable Crowfoot Wrench |
| Precision Armament Hypertap 7.62mm | Timing Nut + 20 ft. lbs. | Spanner | Included (no torque) or Adjustable Crowfoot Wrench |
| Precision Armament Hypertap 9mm | Timing Nut + 20 ft. lbs. | Spanner | Included (no torque) or Adjustable Crowfoot Wrench |
| Precision Armament M4-72 5.56mm | Timing Shims +20-30 ft. lbs. | 0.750″ | 3/4″ Wrench |
| Precision Armament M4-72 7.62mm | Timing Shims +20-30 ft. lbs. | 0.750″ | 3/4″ Wrench |
| Precision Armament M11 5.56mm | Timing Shims + 20 ft. lbs. | 0.985″ | Adjustable Crowfoot Wrench |
| Precision Armament M11 6.5mm | Timing Shims + 20 ft. lbs. | 0.985″ | Adjustable Crowfoot Wrench |
| Precision Armament M11 7.62mm | Timing Shims + 20 ft. lbs. | 0.985″ | Adjustable Crowfoot Wrench |
| Surefire 3-Prong SOCOM Flash Hider | Timing Shims + 20-30 ft.lbs. | 3-Prong or 0.750″ | 3-Prong Wrench or 3/4″ Wrench |
| VG6 Epsilon/Epsilon SL 5.56mm | Crush Washer | 3-Prong | Included |
| VG6 Epsilon 7.62mm | Crush Washer | 3-Prong | Included |
| VG6 Epsilon 9mm | Crush Washer | 3-Prong | Included |
| VG6 Gamma/Gamma SL 5.56mm | Crush Washer | 0.750″ | 3/4″ Wrench |
| VG6 Gamma 7.62mm | Crush Washer | 0.750″ | 3/4″ Wrench |
| VG6 Gamma 9mm | Crush Washer | 0.750″ | 3/4″ Wrench |
Components Required
| Quantity | Component |
|---|---|
| 1 | Upper Receiver |
| 1 | Muzzle Device |
| 1 | Crush Washer or Timing Shims1 |
1: Verify the need for a crush washer or timing shims with the table above or the muzzle device manufacturer’s instructions.
Instructions:
Step U6.0: Remove Existing Muzzle Device (replacement/upgrade only)
If you are replacing your muzzle device (or need to remove the muzzle device for any other reason), first ensure the firearm is unloaded.
Remove the muzzle device using the appropriate muzzle device wrench and threading it off of the barrel.
If your muzzle device is pinned/welded, you may drill the pin out using a drill press.
Remove the crush washer or timing shims, as applicable.
If you are reusing the barrel, clean and inspect the barrel threads once the device is removed.
Step U6.1: Determine Timing Shims Required (as applicable)
If using a muzzle device that requires timing shims, determine the combination required to time the device appropriately.
Step U6.2: “Wet” the Barrel Threads (optional)
For muzzle devices using a lock nut or crush washer, apply high temp grease (e.g. Molykote G Rapid Plus Paste) to the muzzle threads.
For muzzle devices using timing shims, apply several drops of ultra-high temp thread locker (i.e. Rocksett Muzzle Adhesive) to the muzzle threads.
Step U6.3: Install the Muzzle Device.
Install the necessary timing shims or crush washer onto the barrel threads.
Thread the muzzle device onto the barrel. Hand tighten.
Step U6.4: Torque the Muzzle Device
Attach the appropriate muzzle device wrench. Set the torque wrench to the value recommended by the muzzle device manufacturer. If you are using an AR armorer’s tool, be sure to Adjust the Torque Setting appropriately.
For muzzle devices using a crush washer, torque the device to 10 ft. lbs. This is the minimum torque required. Continue to torque until the device is properly aligned, BUT DO NOT EXCEED 20 FT. LBS.
For muzzle devices using timing shims, torque the muzzle device until the torque limit recommended by the muzzle device manufacturer is reached. Note that we do not recommend exceeding 20 ft. lbs. of torque. Never exceed 25 ft. lbs., as this will constrict the bore and affect accuracy.
Step U6.5: Drill, Pin, and Weld (if applicable)
If you will be pinning and welding your muzzle device (e.g. if you are building a non-SBR on a sub-16″ barrel), proceed to the Pin and Weld tutorial.