I have a spare (new, undrilled) barrel and a surplus FSB and was going to send it off to someone to taper pin. Then I got to thinking, will this be as strong or stable enough for use in comparison to an undrilled FSB?  Is the fact that it's already been taper pinned significant?

Only source I know of for an undrilled FSB is ar15sport... Any others? I had a Daniel Defense one a few years ago....

Thanks for any help.

If your spare barrel isn't already drilled for a separate FSB then it shouldn't be too bad.  The guys that pin FSB's for a living should be able to do a good job with it, but worst case is I could see their being a slight gap under/over the pin on one side.  It should still be plenty stable enough, probably no difference really but I am sure others will be able to tell you better then I can.

What I can tell you is there are a few places that offer .625 FSB's.  The first choice for me would be Brownells, they have them for $20. Link - Brownells .625 FSB

Most other places are $30+ for the same thing.  And a lot of them will be F marked as well, BCM offers an F marked one not sure about not F marked.  Fulton armory has some as well but are higher priced, JSE Surplus has some but I believe are the F marked ones.  I am sure I am missing some but that gives you a few options.  For $20 I'd just get a new one from Brownells and not worry about it, I believe most places charge extra to pin one that has already been drilled so you  may even save money by getting a new one?  I wouldn't know, I do my own and only use undrilled ones.

Send it off to JT.  He welds them closed, then redrills them as part of his installation process.  He does flawless work.

Like they said. I'm always on the lookout for used FSB's, I've probably put half a dozen old Colt .625 FSB's on new Citadel barrels and re-parked them. As previously noted, it's not a big deal to put a used FSB on a used barrel either. I have a jig I use to align the barrels and FSB's, then drill them on my Bridgeport.

Before I had the tools to do it, I used ADCO, and they did a great job of putting used FSB's on used barrels. I've never used John Thomas, but I'm sure he does great work, and I can attest that he goes out of his way to help guys on here do things themselves when he could have held out to get the work. I'd go to him in a heartbeat if there was something I couldn't handle myself.

Brownells .625 FSB's. On the one that's standing up, you can see where I'm grinding off the forge flash prior to blasting and re-parking for a retro build.


The jig I use for drilling, with a new Citadel barrel and used Colt FSB to illustrate.


Closeup. This just to show how the jig works. You don't really want to pin an FSB without the handguard cap. Ask me how I know.

It's easy enough to do, and plenty sturdy, if only one of the items is used (especially if you're willing to put up with oversize pins). If both are used that's when it gets a little trickier (since the holes might not be lined up).

I am working on the same project right now. I have both a used colt fsb and a new fsb from Brownells. When the brownells fsb came in I realized that the back of the fsb is not recessed to accept the vintage Colt handguard cap with the lip (fsb side of the cap) so I ordered a new one from Fulton armory which is flat. I did not want to take a grinder to the colt handguard cap. Hope this helps. If I can find the right size bit I might be tackling this tomarrow 

One tip on mounting FSBs:

If the FSB is at all loose on the barrel, clamp it to the barrel when you drill it so all of the clearance is at the bottom. I use a small C-clamp.
Otherwise it is possible that no matter how hard you drive the pins the FSB will still wobble a very small amount on the barrel. And bigger pins WILL NOT cure it.