If your AR has a standard Front Sight Base (FSB, the “A-frame” standard front sight), and you’re wanting to upgrade to a free float rail that extends past the gas journal, your best method is to cut down and reshape the FSB to fit under the new rail.
The milspec style FSB is retained to the barrel via 2 taper pins. This is arguably the most secure method of retaining a gas block, so replacing the FSB with a low profile gas block would be a step back.
We remove the FSB, cut away everything we don’t need (front sight “tower”, bayonet lug, and sling swivel), shape what’s left into a smooth and pleasing shape, then re-blacken it with Oxpho-Blue.
First pic shows the FSB with the bayonet lug cut off.
The the sling swivel cut off.
The rear of the sight tower cut through.
The front of the tower cut through, allowing the entire tower to come free.
The next 2 pics show rough cuts, removing the shoulders left from cutting off the tower.
The next 3 photos show the resulting gas block after being fully shaped by hand on a belt sander.
The last few pics show the finished gas block, after blackening.
