Please refer to the parts guide here for clarification on parts mentioned.
Not Complete, Pictures to be Added
Step 1:
If you haven't already done so, complete steps 1 through 4 of the basic takedown guide located above.
Step 2:
Remove the clamshell handguard. Refer to step 6 of the basic takedown guide.
Step 3:
Remove the barrel extension and/or the flash hider depending on your configuration.
Step 4:
Knock out roll pins #09, #107, #126 from the sight tower.
Step 5:
Flip the rifle over and look at the bottom of the sight tower. Where pin #09 used to be you'll see there is a set screw located beneath it. Remove this screw. Once removed, the sight tower should no longer be attached. Slide the sight tower and gas tube off the outer barrel.
Step 6:
Get out your armorer's wrench and remove the barrel nut and delta ring. Remove the outer barrel by sliding it off the inner barrel. Be sure to keep track of the inner barrel spacer (aluminum) and the brass inner barrel assembly washer. If you can not locate the brass washer, it is probably still inside the outer barrel.
Step 7:
Remove the inner barrel assembly from the upper receiver. To do this, simply pull the assembly straight out of the front of the upper receiver.
Step 8:
To remove the the forward assist, knock out roll pin #32. Once removed, the forward assist assembly will come right out.
Take note the position of the pawl on the forward assist assembly as it will need to be installed in the same way.
You should now have a completely disassembled upper receiver.