When you install a M16A1 never drilled front sight base on a new barrel how do you locate where to drill the holes for the tapered pins? The holes must be located so the tapered pin have the proper engagement with the barrel. Not too little; not too much. Please do not bring up set screws. I do not want nor am I going to use set screw to secure the front sight base to the barrel.

I would just send it to John Thomas at Retro Arms Works.

It also has to be aligned with the pin in the barrel extension so it sits vertical and aligns with the rear sight.


Second recommendation for Retro Arms Works.

ADCO can do this also.

A third recommendation for JT at Retro Arms. He does this for a living.

The recommendations above are completely valid, and will get you outstanding results.

But, if you want to do it yourself, this is from the Technical Data Package.

By chance do you have a copy of drawing B8448575 Tapper Pin.

Getting good alignment of the FSB is much more difficult than doing the pins. The guys that do it professionally usually have some sort of fixture to accurately align it. I've done one myself without anything special, it took a lot of time. I put cardboard on the jaws of a pair of Vise Grips and used them to clamp the sight base to the barrel. I centered the carry handle sight then shot the rifle in by rotating the FSB.

I didn't do anything special on where to position the taper pins. You are right they can be too deep in the barrel or not deep enough, and I know the print calls for +- .005 spec, but in my opinion there is more acceptable leeway for proper function. I eyeballed mine for the center line of the drill to run through the intersection of the barrel and sight base. Then reamed them a little at a time for the pins to seat properly. I am very satisfied with the pin placement. Is it perfect? No, not by any means, but I'm doubtful most would ever know my fists of ham did it without anything special. Alignment ended up 1 or 2 clicks off from true zero on the carry handle. Access to something like a Bridgeport and some tooling could get you within the measurements called out on the print, and I'm sure is how John Thomas and ADCO do it. The pin placement on factory built rifles is ALL over the place for what it's worth.

BRD used to have a jug, but it looks like it may no longer be available

Yes...I do.

OK, you convinced me. Will contact Retro Arms Works and have the front sight base professionally install!

John has super fast turnaround and does great work.

I have the FSB drilling jig, its worth every penny for anyone that does this professionally. That drawing is neat, Its really more a suggestion, +/- .015" is pretty large margin, likely just because they have to put a tolerance on a drawing. Centeredish is just fine. I've installed hundreds of them. More important is to not ream too deep so the pin sits too low on the large side.

Start with a #32 drill bit, carbide, cuts right through nitride finishes because nothing else will.

I done my very first one 3 weeks ago. - https://www.reddit.com/r/RetroAR/comments/1c46cei/diy_fsb/

I will be doing my 3rd one this week. I love to see people working with their own hands and doing their own work. I love to see people learning new things. Id love to see more gun smithers in this world. I wish everyone would try things like this. The older generations were good with their hands. We are running out of them type people. We need more people like John Thomas and John Norrell in this world. That said, it is easy to mess it up. From getting the sight canted to drilling it wrong to reaming it too deep. I used a cheap barrel that if I messed up, I would have just threw a regular gas block on and used it for another build. I always knew there were a 50/50 chance of something going wrong. Read a few how-tos online then decide if it is in your ability and skill set to do. Also consider the possibility of messing up. Is the barrel and FSB cheap and replaceable? Are you willing to accept messing it up? Do you have the means and tools to do it? There are guys on Reddit doing FSBs just for tips. There are people like John Thomas doing it 100% right for a very fair price and a quick turn around.

DIY A2 FSB Install- Version 2.0

Had JT do my dedicated 22 upper. He does great work.

Mailed it to him on a Friday, he received it Tuesday and shipped it back the same day.

I wish I'd have cut that damn bayonet lug off before sending it to him. Would have been a lot easier off the barrel.