How to pin an AR-15 front sight post

Cole2534 · Aug 18, 2016

I did one of these last night but I don't think I did it the best way. I took some measurements and leveled the front post with the bore CL and went to reaming.

How else do people do these things? They're a fairly rough forging, so there's not much (if any) of a place to put an indicator.

abarnsley · Aug 19, 2016

That flat cut in between the front sight ears (FS removed), is a handy place to make a jig to fit.

FSB jig | BRD ENGINEERING

And a one off method..
FSB Drill Jig? - AR15.COM

Considering that the barrel extention locating pin, allows a degree or so of movement in upper receiver slot... An indicator might be a bit overkill/underperforming in real world...

And especially so, when rear sight is adjustable...

Butch Lambert · Aug 19, 2016

From the Long Range forum.

http://www.usrifleteams.com/forums/index.php?showtopic=31162

Cole2534 · Aug 22, 2016

Thanks for the replies, I'll have to view them from home. Apparently gun websites are against our new weapons policy. lol

Gazz · Aug 23, 2016

I have done them by inserting the barrel in the upper receiver and then clamping the bottom of the receiver to a flat and level surface. Apply some superglue to the barrel avoiding the area around the gas port. Slide the front sight on and adjust by eye or use a square on each side of the sight tower to get properly aligned. Let the glue set up, check for a clear gas port and then carefully drill, ream and pin one hole and then do the other. So far no problems with sight alignment or gas flow. Somebody may curse me down the road for the glue but a bit of heat will get by that.

Cole2534 · Aug 23, 2016

The BBL I drilled was already in the upper receiver so I put the BBL in a v block near the gas block register and then used a DTI to get the receiver horizontal. I then found the BBL CL and used a jack to bring the sight post up to the CL where I clamped it tight. I put the DTI on the front sight to see if it was moving as I was drilling but it only wavered a few thou throughout and when the operation was done it settled back to within 0.0015ish of it's original zero. That should be close enough that the rear sight's adjustment will be very near the middle.

Cole2534 · Dec 14, 2017

Gonna necro-bump my own thread because I am going to do it again.

This time I'm going to pin a gas block on just a barrel, so here's my plan-

After taking some diameter measurements set the receiver extension and the muzzle on some vee blocks, straight and level. Then I'll use a stack of Jo blocks to get the index pin rotated to vertical and clamp.

From there I'll repeat the jo block process from a datum on the gas block and clamp it as well.

Locate holes, spot/drill/ream/pin.

Anyone see any glaring flaws in this plan?

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How to pin an AR-15 front sight post

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