Quoted: Now for the next part......
I have put the barrel nut on, handguard cap and slid the FSB on. I trued it up as best I could with an upper and a square. I need some advice on how to secure the FSB to the barrel. The taper pin holes almost match, but it leaves the handguard cap loose. How should I proceed?
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You are missing the really important part that everyone learns when they get to the point you are at in replacing a front sight base...
Front sight bases and barrels are drilled/reamed/pinned as an assembled pair.
There is no spec as to where they get pinned as it does not matter.
They are not meant to be swapped around.
If there is a problem with the front sight base, you just replace the whole barrel assembly.
Now that we have that behind us, here's what you have to do...
Remove the rivet holding your sling swivel to the front sight base.
Tap the hole that's revealed for a setscrew, whatever size you have that works is fine.
Install the barrel on the receiver.
Install the front sight base on the barrel and slide it back against the handguard cap good and tight.
Make sure it's aligned straight up, there are sight alignment bars you can buy if you are working with an A1 or A2 receiver.
Tighten the setscrew to hold the FSB into place.
Take the barrel back off the receiver.
Set it up in the milling machine so you can drill down through the front sight base AND barrel in one operation with an endmill.
A drill bit will simply follow the two mis-aligned existing holes.
You will need to go oversize a couple sizes.
Factory taper pins are 2/0.
You can go to a 5/32" spring pin or a #0 taper pin, your choice.
www.mcmaster.com has taper pin reamers and taper pins.
You will likely have to shorten a 1" long taper pin as you will not find the proper 13/16" length easily available.
Ream the depth as required to make the head of the taper pin just above flush.
Shorten the taper pin from the small end.
Do the front pin completely, and install the pin, then remove the setscrew and do the rear pin.
Good luck on your adventure.
I do everything on AR-15 barrels, but I hate front sight base work...
Randall Rausch
www.ar15barrels.com