Issues with replacement (Overview):
Replacing the AR-15 gas block (or front sight base) comes with issues as the gas block is mounted to the barrel and drilled during assembly. This means that the gas block is placed onto the barrel and drilled through the gas block and barrel. The holes are then reamed to size with a tapered reamer and special tapered pins are installed.
Removal of the AR-15 Gas Block:
To remove the gas block it will be first necessary to remove the two tapered pins from the front sight base. This is done by driving the taper pins out with a pin punch. The tapered pins are removed by driving from left to right; the small end is on the left side of the barrel, the large end is on the right side! It will often require considerable force to get these pins out but with olid blows in the correct direction they will come free! After the pins are removed the gas block will slide off the barrel.
Replacing the gas block:
Because the gas blocks are drilled while mounted to the barrel the holes on two different gas blocks are not likely to have their holes drilled in exactly the same location or angles. The place to start is by installing the new gas block to the barrel and look at the alignment of the holes through the front sight base. With luck, you will be able to see the holes in the barrel through the holes in the new gas block.
From there, I like to tap the hole on the bottom of the gas block for a small set screw and take the weapon to the range to confirm that the cant of the front sight is correct. I am sure this could also be done with loc-tite but with the set screw it is easier for me to make adjustments and keep the gas block from moving when I have it where I want it. I will also scribe a small mark on the barrel.
To install the new gas block, drill out the taper pin bores. I have not done a gas block replacement in years but I believe I used a 3mm drill bit but what is important is to try to use a bit that is about the same size as the original "SMALL" hole in the original gas block and barrel. After the hole is drilled, ream the hole with a taper pin reamer until the newly reamed hole is deep enough to allow the taper pins be fully engaged and drive the taper pins back in.
Where to buy the tools:
Brownells:
Front Sight Base Taper Reamer: PN: 080-726-004
Front Sight Base Tapered Pins: PN: 080-725-001
http://www.brownells.com/aspx/NS/sto...il.aspx?p=5613
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