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.