I have heard that it's not possible to replace your front sight base with a different one because every barrel has a slightly different diameter.  I want a standard AR15 bayo lug fsb on my old post ban barrel.  Is it possible or not?  Thanks!

Jon

The FSBs are generally in standard sizes .75" and .625".

It will be the taper pins where the problem lies.  There is no standard as to where the taper pins are to be placed, so every barrel is drilled differently.  Sometimes you might get lucky and find a FSB that has been drilled to match another barrel, but it's very rare.

You can buy un tapped FSBs and try to install them, but it requires some sort of Jig.

Best way to go if you don't have an FSB and don't want to mess with installing one is a railed gas block that uses set screws.

EDIT:  Reading the question again, one way might to be buy an Armalite FSB gas block with a bayo lug adapter.

If your handy at welding, you might try welding an FSB onto the gas block?

It's probably not something that you could do yourself, but I think ADCO does it all the time.  Call them and ask about it.  

In fact here it is listed on their site under "shop services" for $85.

FSB Install: No-Ban FSB on your .750 barrel  $85.00 We supply and install a bayonet lugged FSB onto your barrel. Same price to drill/pin a customer supplied FSB.

www.adcofirearms.com/shopservices.cfm?page=shop

Quoted: Best way to go if you don't have an FSB and don't want to mess with installing one is a railed gas block that uses set screws.

Don't do that. I had one on my Dissy and when it heated up the screws came loose and the FSB flew off. I drilled holes going vertically so I could attach it the way the normal FSBs are attached and It has worked good so far.

Quoted: Quoted: Best way to go if you don't have an FSB and don't want to mess with installing one is a railed gas block that uses set screws. Don't do that. I had one on my Dissy and when it heated up the screws came loose and the FSB flew off. I drilled holes going vertically so I could attach it the way the normal FSBs are attached and It has worked good so far.

Right, most Armalites come standard with a railed FSB.  I've shot 10K+ rounds through them without any problems.

Thanks for all the info guys.  I appreciate it.