AR front sight replacement

[Spray-n-pray]

I just read on ARFcom that it is not.possible to use a front sight base on a barrel that has already been drilled for a base. Does anyone know if that is true?

http://www.ar15.com/archive/topic.html?b=3&f=118&t=553340

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[ZigZagZeke]

What they are saying over there is that the two locating pin holes for the pins that hold the base in position are drilled after the block is assembled to the barrel, and not always in the exact same location. I don't know whether that's true or not. It's kind of hard to believe. I'm sure the holes are drilled by a machine with the barrel assembly in a jig at the factory. Seems like they would always land pretty much in the same place. If it is true you could go the permanent Loctite 262 route. On my Bushmaster they used Loctite 262 to hold the gas block in place. When I changed gas blocks I had to use a torch to heat the gas block and barrel to 500 degrees or so, then tap it with a hammer and drift punch to slide it off the barrel. The heat softens and releases the Loctite. I would think that if Bushmaster holds gas blocks in place that way, without any other clamps or screws, that it would work for a front sight base too, even if you mount a bayonet to it.

 

[eldbillbo]

some brands will mate up with their own brand , so if you have a fsb off a colt its a good chance it will fit another colt although they did use different pattens from M16 barrels to Sp1 lw barrels but if you have for example a colt M4 barrel and got a FSB from another Colt M4 or Tac carbine it should fit. I have also had bushmaster fit bushmaster and stag fit stag ect they just will not interchange between brands. there are exceptions where it may not be exact meaning the holes could be off a little but it appears each company uses the same jig for their company and usually the are not the same for another company for example a bushmaster jig is not same as colt so the taper pin holes will not be the same. But i usually have had good luck mating colts to colts

and keep in mind depending on brand there may be exceptions to this for example if a company changes tooling or out sources their barrels or barrel parts.

you would think they could all use the same jig and make it easy

 

[Velzey]

I've seen allot of the colts interchange ... But not colt to bush or dpms etc.

That's why you see some front sights not drilled for the cross holes. I've replaced a few with the base pre drilled and reamed and it's looked like it lines up perfect ... Press in the pins and then gently tap the sight side to side .. Yep it moves...
Couple things you can do if it lines up but moves slightly, is drill and tap the underside for a couple set screws and then use red locktite...

 

[JBRC]

Yes, it is possible to use a new un-drilled front sight base on a barrel that has already been drilled for a base. We have used this trick many times to fix this problem.

Set rear sight to center. Clean front sight and barrel with acetone. Slip new front sight onto barrel don't forget the front handguard retainer ring. Align the front sight vertically. A laser bore sighter works best to ensure that front sight lines up with the centered rear sight. Once in alignment apply some Loctite 290 wicking grade (green) to the edges where the barrel goes through the sight. Let it cure. Drill new hole .075-.100 further forward than the old......I think I use an 1/8" drill but would have to check on that. The drill will break into part of the old hole, but thats ok keep going until it comes out the far side. Use your taper pin hand reamer to finish up the hole and install pins.

Good luck!