Upper Receiver Assembly

• Barrel Specs:

Barrel produced from Douglas blank

Material: 416 Stainless

Barrel extension: M4 feed ramps

Chamber: optimized for use with MK262 (Black Hills 77gr equivalent)

Twist: 1 in 7 right hand

Contour: for use with OPS inc.

Length: 18 in and threaded 1/2x28

Weight: 2 lbs 6.3 oz

Finished with KG Gunkote - dark gray

• target crown
• Barrel dimpled for set screws

• Barrel markings
• Vltor upper receiver was an excellent fit. It slid onto the extension with slight resistance and was tapped into position for the last 1/8" with a nylon mallet. Fit between the Vltor and BCM4 Upper receivers was almost identical. That honestly says an awful lot about the BCM4. It's a very well made forged upper that is definitely held to better tolerances than the average forged upper. I used the Vltor because I've had good success with them in the past and the aesthetics are a bonus.

• Mounted the upper and barrel on the Geissele reaction rod. All assembly procedures were completed on the GRR.
• Umbrella Corp 33 MS milspec anti-sieze used for barrel nut installation.

• Apply anti seize to the upper threads. Grease also applied to the front of the barrel extension shoulder. If you've ever dealt with a barrel nut that was over torqued, you know that there can be a great deal of stiction between the upper, barrel extension and barrel nut. Application of a small amount of anti-sieze to the front of the extension shoulder can ease disassembly.
• Grease roughly spread onto threads

• Barrel nut is threaded on/off in order to evenly distribute anti-sieze.
• Barrel nut torqued on / off 3 times per the TM in order to mate the threads. Installed at 40 ft/lbs per the Geissele instructions, using their included barrel nut wrench.

• Barrel nut installed

• Barreled upper

• Oil applied to gas block journal. This eases installation and prevents corrosion under the gas block. The gas block journal and BCM gas block were both very well toleranced. Very tight fit, but did not require a hammer to install, nor would it slide around easily.
• Gas block slid into position. Note, a small gap is left between the barrel shoulder and the block. The barrel is relieved for a handgaurd cap and the block should be spaced as if the cap were in place in order to attain good gas port alignment with the gas block.

• Note barrel dimples aligned with screw holes on gas block
• Note, set screws supplied by BCM are knurled. This is preferred, as the knurling bites into the barrel dimples and provides a more secure attachment. Screws and gas block threads have been degreased.

• Gas block is double checked for vertical alignment before installing set screws. Screws are then inserted, with one holding the block in position. Loctite (red 272 / high temp) is applied to the other and then installed into the gas block.

• Gas tube is slid backwards into the upper receiver and then forward into the gas block. Tube port is oriented down.
• Tube is pushed forward into the gas block, making sure that the hole in the gas tube is aligned with the hole in the gas block. Note, daylight is clearly visible through the hole in the gas block.

• One of the best features of the Geissele SMR rails - no alignment necessary!
• Insert gas block roll pin into Geissele roll pin tool. Tool will retain the pin

• Start pin into the gas block.
• Tap in until tool bottoms out

• Pull tool away, pin will be retained by the gas block.
• Using a roll pin punch of appropriate size, fully seat the roll pin.

• Stripped carrier is inserted into the upper to ensure that the carrier does not bind on the gas tube.
• Barrel gets a light coat of Fireclean brushed on before the rail is installed.

• Rail is slid over the barrel and started onto the barrel nut
• Rail is slipped into final position and roughly aligned by hand.
• Bolts installed through rail into dogbone nut. NOT tightened yet.
• PRI alignment tool is installed and clamped down to perfectly align the rail and upper receiver.
• Bolts are snugged up hand tight, per the manufacturer instructions.

• Geissele SMR rails all feature a secondary anti rotation feature, seen here as two small screws, near the receiver. They are torqued finger tight. Once installed, the rail is extremely rigid.

• Muzzle device installed to specified torque with Rocksett. And DONE!