Turning a AR-15 Front Site Block into basic Gas Block

Removal and modifying an AR-15 FSB to become a basic gas block that will run under a mid-length free floating accessory rail. We're not responsible if you do yours and screw it up based on what you read here.

I got together with the Outdoor Bros. yesterday to help with and to get some pictures of the process to cut down and modify a standard AR-15 front sight block. Doing this is a cheap way to run a longer rail on an AR-15. First the basics. Upper is a LMT 10.5" that will be mated to an SBR lower once the paperwork returns. The rail to be used is a 9" Daniel Defense rail.

First job is to remove the flash hider. You should replace the compression washer when the job is complete. You can probably get by re-using the existing one.

Click on the pictures for a larger view

First we knocked out the rivet attaching the sling hanger. Probably better to remove it early before cutting to keep it from possibly being launched by the cutting wheel.
Here the sling hanger and flash hider have been removed.

Full view with the upper properly held in the vise with an proper upper vise block.

Next drive out the two pins attaching the FSB to the barrel.

Using a small roll pin punch, drive out the gas tube retaining roll pin.

Once the three pins are out you can slide off the FSB and handguard plate (which will not be going back on). One of the very few negatives about LMT AR-15's is that the barrel is not parkerized underneith the FSB. We're going to degrease and cold blue the bare metal of the barrel and inside the FSB before the job is done.

FSB is now mounted securely in the vice and ready for the cutting wheel.

Why wear yourself out using a dremel tool when you have a proper grinder with a cutoff disc. This tool made short work of removing the hanger bracket and bayonet lug. Protective eyewear and hearing protection was a must during this process.

A picture to make Bill Clinton and Diane Feinstein happy. Bye bye Mr. Evil Bayonet lug.

Next goes the site tower. Don't forget to remove the site for your spare parts kit.
Here the site tower, bayonet lug and sling hanger lugs are removed and some of the additional material removal has begun. It's a tight fit to get the Daniel Defense rail over the gas block for installation. A good amount of metal has to be removed from the top and bottom of the block.

You only want to remove enough material to be able to install the rail. Rick stopped frequently to check the fit. The top of the gas block is just about done here.

Here the bottom is finished. Basically the bottom gets rounded off which also means that the retaining pins will hang out too far for the rail to be fit also. (LMT uses pins that are beveled on one side making it easier to start tapping them in). We wanted to cut the non beveled side of the pins. They were tapped into place so the bulk of the amount to be removed was left hanging out. Rick then started the cuts to keep the pins squared off. Tapped them out a bit and finished cutting them off and deburring them. You want them cut off square so you have a flat surface so your punch won't slip off when you put them back in.

Job is basically done. The gas block still needs to be refinished with Brownells baking laquer or Brownells Teflon molly bake on finish to give it some durable protection. You can spend a lot of time making it all super smooth and all. Why bother? Leave as much material as you can and have it fit. Get rid of any sharp burrs and finish it. It doesn't have to be pretty hiding out of sight under the rail.