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Posted: 12/20/2003 5:53:39 PM EDT
Hi all,
I have a problem:
I have a post-ban barrel and I need a pre-ban configured frnt sight base (with bayo lug).
I know that there is a difference in pins position (right?).
My question is:
Can I find some kind of pre-ban configured front sight base with post-ban pin holes somewhere? If Yes Where?
If No, how can I do?Any suggest?

Thank You very much.
Mauri
Link Posted: 12/20/2003 6:55:40 PM EDT
Not that I am an expert but I am pretty sure that you can just get a preban FSB and attach it.  I don't think the pin locations are any different.

Jbritt
Link Posted: 12/21/2003 2:44:20 AM EDT
Thank You very much!
I live in Italy so I have some problems to find this kind of informations.
I ordered a preban FSB from US, but the pins holes were in a different location...maybe I was unlucky.

I'll try again asking to the seller a FSB with my barrel holes position.

Thanks again.

Bye
Mauri
Link Posted: 12/21/2003 3:22:09 PM EDT
[Last Edit: 12/21/2003 3:23:01 PM EDT by mongo001]
Here's what I've done with great success.  You drill and tap the original pin holes.  The drill size is #29 and the tap is #8-32.  You get 1/8" or 3/16" (length) setscrews (the 3/16" may have to be shortened a little) and install the base with the setscrews and Loctite 222.  I saw this at www.fultonarmory.com and read about this in some books about accurizing AR-15s.  With properly sized setscrews, the installation is completely unnoticable unless you know what to look for.

Fulton Armory sells one for $59.95, but you can usually get a sight tower for around $20 and setscrews for about $0.10 each, and a little bottle of Loctite 222 may be $10 or so.

Fulton Armory puts it this way:

-"Allows front sight windage adjustment so you can zero with the rear sight aperture centered!"

-"Tangent opposing set screws wedge incredibly tightly; this front sight base won't move, yet you can loosen the screws & and reposition the base if needed."

You can just about put any sight base on any barrel with this method.  I use this very often to put mismatched sight bases on different barrels and it works great.  I have not yet tried to center the sight post in my windage adjuster (seems like too much work for the benefit), only do that if there is a gross error that needs to be fixed.  A little Loctite 222 ensures the setscrews won't back out on you, but allows for removal if necessary (Loctite 222 isn't "permanent" like some Loctites but holds extremely well).

Good luck in your efforts.
Link Posted: 12/22/2003 3:58:31 AM EDT
[Last Edit: 12/22/2003 3:59:12 AM EDT by BookHound]
Originally Posted By JBritt:
Not that I am an expert but I am pretty sure that you can just get a preban FSB and attach it.  [red]I don't think the pin locations are any different.[/red]

Jbritt
View Quote


This is [b]NOT[/b] correct.  The pin locations are almost always different.  If you find another FSB assembly that does perfectly match, you got very, very lucky.  Also, try ordering a FSB assembly from anyone with holes already drilled.  I couldn't find any company that sold them with holes already drilled.

mongo001 is correct, you will need to drill and tap new holes.  Armalite makes a FSB assembly that attaches with two screws under the barrel; cost is $43.50.  I recently got one of these and am very happy with it.


Edited to add the Armalite base I got is post-ban.  Don't know if they have one that is pre-ban.
Link Posted: 12/22/2003 8:14:10 AM EDT
Thank you very much for correcting my mistake.  I have only seen one FSB replaced and I guess we got very lucky.

So basically when I change my FSB after next september I will need to order one with out predrilled holes and then have them dilled to fit the BBL?  

Thanks,
JBritt
Link Posted: 12/22/2003 8:30:26 AM EDT
No problem.  Until two weeks ago I thought replacing a front sight assembly would be a cheap, trivial thing.  Boy was I wrong.  [:D]

Yea, you'll have to drill the holes yourself.  I think next September all my rifles will be getting flash suppressors, but I doubt any will get bayo lugs added.

I will be hosting a barrel and buttstock swapping party though.  [;)]


You know, I'm really shocked that there isn't some kind of spec for those damn FSB holes.  It would make things so much easier.
Link Posted: 12/22/2003 4:57:09 PM EDT
Seems like the only spec is that each sight base must have two holes, one on each side.  Drill wherever you feel like that day.  I have yet to get a good match on FSB swap.  I've forced a few that were close, but the results were ugly.  One word of caution --> tap these holes SLOWLY --> getting out a busted tap sucks.  Use cutting fluid liberally.  Save yourself a headache on me.
Link Posted: 12/23/2003 3:27:47 AM EDT
Thank You guys, I found something about FSB:
http://www.funsupply.com/Firearms/m16sight.html

I didn't know It was so hard to fit a new FSB.

I'd like to change my barrel assembly, but I cannot find It here in my country.
My barrel is heavily damaged, I shot a round with a bullet fit in the barrel :,,,,-(
My rifle accuracy didn't decrease, but I'd like to change It.
Italian Colt importer sell me only post ban barrels...but I want a preban one, in order to have the FBS with bayo lug (for the flash suppressor It's not a problem, my gunsmith is really good).
We have no laws about pre and post ban rifles here, but I cannot find what I want.

I'd like to import It from US directly, but It's not so legally :-/

...
but I'd like to try :-I

However, thanks again guys...
Another thing that I've learned about this great rifle!
Link Posted: 12/23/2003 5:54:19 AM EDT
Well, after the AWB dies I will be having a "get my upper and telstocks from my moms house and mate up my postban lower party!"  

I talked to Kurt @KKF and to change out the brake and FSB and add a FSB with boyo and a Vortex will be $115 for parts/labor.  So I guess my posty will go to him next sept.

Weldox, good luck on your project.

JBritt
Link Posted: 12/23/2003 5:23:38 PM EDT
You should be able to get a front sight base from any of the major manufacture's, Olympic, DPMS, Bushmaster etc. They usually cost around $ 35 US.
Indexing it onto a barrel right is another story ! The easiest way is to tap the hole beneath the sling swivel for a set screw then install front sight base just eyeballing for windage than shoot it at 50 meters or so using the front sight base to make windage adjustments untill you have a good mechanical windage zero than tighten the set screw and use Loctite ( Industrial fastener glue )on both rings to hold it. after a few days you can cross drill through the Front sight base and barrel and install a regular roll pin.
Link Posted: 12/23/2003 6:06:33 PM EDT
tangeant, that's a great idea.  Thanks for the info!
Link Posted: 12/25/2003 9:22:27 PM EDT
[Last Edit: 12/25/2003 9:41:06 PM EDT by mjcarter]
Weldox,
 This is a long post, but here goes. My first recommendation is just go with the post-ban setup you already have. Front sight bases are located and then drilled and taper reamed on each individual barrel. No two are the same unless they are done on the same equipment and even then it may not be exact.I have a clamp-on AR15 front sight base from Armalite. They work very well. Has two socket head cross bolts. Locks up solidly and you can even use some red high strength loctite (make sure it is where you want it because this stuff takes about 400 degrees f. to loosen) to really fasten it down. Squirt some compressed air through the gas tube to be sure there is no locktite in the gas port. Looks just like the factory sight and (for U.S. shooters)is approved for CMP competition. However, it does not have a bayonet lug. If you get another pre-ban factory sight, it will need to be located and drilled. Roll pins are not as good as taper pins. I've had both kinds. Another person suggested using set screws. Since the new barrel is already drilled, the set screws will go into the cross drilled holes and not do anything positive for windage adjustment, so forget that. To use set screws properly, there must be 4 small flats milled into the barrel for the screws to ride in (on undrilled barrel). When drilling and tapping a sight base for the screws, the holes need to be located slightly higher up than where the taper pins go. This allows full bearing of the screws in the milled flats. Properly set up, the set screw sight is great for a target rifle. Your new barrel is already cross drilled, so your gunsmith can use a new undrilled front sight, or the old one if the holes are really close, but you already said they did not match. He will most likely have to go a tad oversize with the drill and tapered reamer to clean up the existing holes, but taper pins come in many sizes and are readily available. Tangeant described the way to index the front sight for windage prior to drilling. Tap the hole below the sling swivel for a temporary set screw, center the rear sight for windage, install front and shoot to confirm windage, then locktite the front before drilling and installing crosspins.  I don't like them, but Bushmaster makes a bayo lug that clamps around the barrel in front of the sight base.
Link Posted: 12/27/2003 1:22:03 AM EDT
I decided that the best choice is to buy a new pre-ban barrel assembly.
I think It's the easiest and best thing to do.
Probably I'll buy It direcly from US...
I'll try to buy It.
The worst thing that can happens to me is to lose my money...nothing else (no law problems).

Thank You guys.
Bye
Mauri

Link Posted: 12/28/2003 9:47:41 AM EDT
Good choice. I thought you said that there was an importation problem.
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