New FSB install on an old barrel?

[deviljon]

I currently have a barrel with a chopped front sight into low profile gas block. After giving it a lot of though, I want to go back to a good ol A2 FSB. Obviously, the original one can no longer be used since it's been hacked.

If I were to install a new front sight on the barrel while re-using the old FSB taper pins, would it be a problem? I understand new FSBs on new barrels require a special procedure, would this require the same?

[CIV Tactical]

this should not be a problem. Simply remove the hacked fsb and align the new one with the taper pin cuts in the barrel. this should keep you in alignment. hope this helps

[kcstott]

Since AR parts are built to better tolerances I'd say you should be good to go. But you might run into a slightly misaligned hole.

[kendog4570]

Using the holes in one base, and the holes reamed into another barrel, especially from a different provider, the chances that it would line up to within 8 MOA either side of your rear mechanical wind zero are slim to none.

[deviljon]

Using the holes in one base, and the holes reamed into another barrel, especially from a different provider, the chances that it would line up to within 8 MOA either side of your rear mechanical wind zero are slim to none.

Are you saying that regardless of what I do, the front sight is going to be extremely canted? Is there any way around this or is it just something that comes along with replacing a fsb?

[kcstott]

Don't use the tapper pins drill and tap the bottom and dimple the barrel.

8 MOA is .035" over 15" so you'd have to be .035" off from top dead center to run out of windage. Which would not be hard to do if the holes were off a touch. Your front sight is .062" wide give or take so you have to be within half that width

[kendog4570]

Are you saying that regardless of what I do, the front sight is going to be extremely canted? Is there any way around this or is it just something that comes along with replacing a fsb?

The pins only have to hold the sight base on, and the different makers dont have to stick to a rigid spec on where they put the holes, and which direction the taper goes. Therefore, unless you have a used FSB from a Colt (or other) barrel, and a FSB from another Colt that was made relatively close in time to each other, the are most likely to not line up.
I repair these all the time for NRA highpower competitors. A lot of new "ready to race" guns are not really ready for much. I have a method and procedure where I can take any sight base and any barrel, regardless whether they have been on another barrel or not, or been taper reamed for another FSB or not, and pin them to within 1 moa of mechanical wind zero. It will stay put, hold zero, and not come off ever. Until you want it to.

[Pro2ndAm]

New FSB on old barrel

Since your barrel and existing FSB were drilled and reamed for taper pins, they sort of have a "unique" relationship. So what you'll need is an undrilled FSB and there are several vendors who sells these undrilled FSB. Unless you're really mechanically inclined and can align the FSB with the index pin on the barrel extension, this stuff is strictly for Smiths or builders with special jigs, drill presses. I've seen some coffee table plumbers do it with a handrill or worst yet, try to use a "take off" FSB and try to fit it on a barrel that has been drilled and reamed for taper pins. Only to see their posts on board as to why they have to crank the windage knob all the way to the left or right and still can't get a mechanical zero.

Just my 2 Cents!

[kcstott]

You just an FYI but on custom rifle with a fixed front sight they twist the front sight to center the windage on the rear. it's usually not much. But on a M4 with a 15" sight radius 1 MOA is .004" give or take. So thats how close you need to be with a firm mount.

[kendog4570]

I use an optical collimator to set the front sight for zero and can get to within 1 moa. Usually less, but I claim 1 to 1-1/2 for "contingencies".

[deviljon]

I'm kind of worried now. I don't want to end up with badly canted front sight because I honestly don't know how capable my gunsmith is with this type of stuff.

Considering just installing another rail and saving the front sight configuration for a later build.

[kendog4570]

I'm kind of worried now. I don't want to end up with badly canted front sight because I honestly don't know how capable my gunsmith is with this type of stuff.

Considering just installing another rail and saving the front sight configuration for a later build.

You can ship it to me and I can do it for you. I charge $85. It WILL be right.
FFL licensed and insured. 25+ years US service rifle experience.
Thanks
Ken

[Pro2ndAm]

I'm kind of worried now. I don't want to end up with badly canted front sight because I honestly don't know how capable my gunsmith is with this type of stuff.

Considering just installing another rail and saving the front sight configuration for a later build.

I echo your sentiment ... there's always another build on the horizon.

[kcstott]

I use an optical collimator to set the front sight for zero and can get to within 1 moa. Usually less, but I claim 1 to 1-1/2 for "contingencies".

I clamp the barrel in the mill vise and use a wiggler. Indicate the rear sight and dial over to the front. It's over kill but I don't have a collimator. It is on my wish list though. Two paths to the same result.