AR Front Sight Question

[Heatseeker]

I'm just finishing up my first AR A2 build. In installing the front sight, I've run into a problem. On the barrel, the two retaining pin notches appear to have been cut with a file. When I slip the sight into position, the the holes nowhere near align. If I move the sight around to get a retainer pin started(just barely started!), the sight is way off to one side.

Is there an easy method to aligning and pinning the sight block? Being a machinist, I'm thinking about making up an index block to mount the barrel into(using the barrel alignment notch as a reference to pick up true 90*) and fixing it to the mill table to make the notch cuts precisely. Of course this will require me to disassemble the weapon and will take a lot of time and machine work. If there were an easier way, I'd sure like to know what it is.

Thanks in advance.

[kj]

I may be mistaken, but I believe that the front site base holes and barrel notches are drilled in one operation. It may be difficult to find a front site base that will line up with the existing barrel notches.

You can tap the front site base holes and install hex-head set screws, like a windage adjustable NM site base. Or, you can buy an A2 site base that clamps around the barrel - I think I remember hearing that Armalite sells one.

[Heatseeker]

Thanks for the reply.

I did think about and was trying to avoid set screwing the base. But the more I thought about it, the more I figured it would be fine for a bit. So that's what I did.

I will order a clamping base in the near future, thanks for the heads up on that!

[ar15barrels]

Sounds like you are installing a different front sight base than the barrel was originally drilled for.
Barrels and front sight bases are drilled as mated pairs.
There is no real spec on pin location so the bases are not interchangable.
As far as Colt and .gov are concerned, if the FSB is fubar, throw away the barrel as it's an ASSEMBLY, not a PART.