I'm building a flat top carbine and am wondering if I need an F marked base.  If so, where in the hell do you get them?  I found them at Bravo Co., but they aren't drilled for the taper pins.  Any ideas?

1)  Buy a barrel with a forged FSB already on it?
2) Get one of the folding FSBs
3) Lurk gunshows and forums untill one turns up used (They do sometimes)

I've got a barrel already, with a FSB, and its ugly - I'm gonna change it anyway.  It seems that if so many new barrel assemblies have the F marked FSB, why aren't they available?  *Ahem* why aren't they available WITH THE TAPER PIN HOLES DRILLED?

In addition to what Bravo said.  I think they drill the taper pin holes through the FSB and the Barrel at the same time to make sure they stay in alignment?  No??

Gundraw

ETA: If I were you (and you don't just wanna refinish your old FSB), I would just look at the set screw options out there.  The key is to put little dimples in the bottom of the barrel where the set screws will land, and then Red loctite (IIRC) the sucker on there and it should keep it from doing any kind of moving around.

First - thanks for the responses.

GunDraw - refinish my FSB?  Is there a higher front sight post that would fix this without changing the base?

So I could take one of the F marked FSB and drill up through the bayo lug?  That seems a little better to me - and the rear of the base already has a hole underneath the swivel (at least the one on the barrel does) - which could be tapped for the set screw?

Since my barrel has a FSB already drilled/pinned in place, the channels from the old pins would help to align the set screws?  I'm liking this more and more...as long as drilling through the bayo lug would be cool.

Quoted: First - thanks for the responses. GunDraw - refinish my FSB?  Is there a higher front sight post that would fix this without changing the base? So I could take one of the F marked FSB and drill up through the bayo lug?  That seems a little better to me - and the rear of the base already has a hole underneath the swivel (at least the one on the barrel does) - which could be tapped for the set screw? Since my barrel has a FSB already drilled/pinned in place, the channels from the old pins would help to align the set screws?  I'm liking this more and more...as long as drilling through the bayo lug would be cool.

Just go to bushmasters website and buy the Front Sight Post that is .040" taller for use with your NON "F" marked FSB...Problem solved for only $5, BUT  buy some other stuff to make the shipping worth it


ETA: Front Sight Post

Yes, you can use a standard FSB.  I actually have the "taller" post in my Varminter (I have/had a BUIS system on it) to use with an ARMS 40.  I have bushmaster's unit that gunnut03 pointed out.

I don't know much about trying to set screw a pinned FSB though, I guess it might work....

Here's the deal, there are two different kinds of FSB (AFAIK) pinned and set screwed.  Basically, the only FSB that come pinned are those that are on the barrels from the factory (most standard FSB) as Bravo pointed out, they come with the barrel for a reason.  However, all the aftermarket FSB (like the railed gas blocks, or flip up ones) have set screws along the bottom of the base. The rumor is that they are much less durable (shift or or twist from impact) in combat situations.  However, I've talked with a few qualified sources, and they assured me that when installed correctly (dimples and loctite), they are very durable.  

This is what I meant by using a set screw setup.  Maybe there IS a standard "F" FSB that uses set screws, I'm not for sure.  But there certainly are other options.

Gundraw

Hmmm...$5 sight post or change the FSB...

Has anyone tried putting a GI FSB on a barrel then set screwing it from below?  Like through the bayo lug and the hole underneath the swivel?  I kind of like that idea...

Quoted: Has anyone tried putting a GI FSB on a barrel then set screwing it from below?  Like through the bayo lug and the hole underneath the swivel?  I kind of like that idea...

I did this exact thing!  i drilled and tapped the bayolug and the hole under teh sling swivel.  I want to say i used 8-32 setscrews.  i then cut some old taper pins up and stuck them in the holes to simulate the pins being there.  i then put on my BUIS and set it for windage zero.  then I shot and adjusted my FSB until it was zeroed.  added a little loctite 190 and it was done.  easy as pie.  

Machinehead,
Did you drill into the Barrel so that the set screws would seat into something?

they lined up with the slots from the taper pins.  i didnt add anything else.

Machinehead - did you put a drop of loctite under the set screw or on the threads only?

i added loctite 290 after the windage was adjusted for mechanical zero.  it is a wicking grade of loctite designed for use on preassymbled parts.  i added it to both of teh barrel bands on the fsb and to both setscrews.  i havent had a problem with it moving.

So, if you didn't have a barrel that had already had the taper pin channels drilled and an F marked FSB - one could drill the bottom of the FSB, and then into the barrel slightly (once you had the windage corrected) and set screw + loctite?  Sounds good to me.  If only they weren't on backorder.

www.bravocompanyusa.com/IronSights.html

sounds about right to me