Thanks Clint.
I started with a new/stripped DD 14.5 M4 barrel and F-style FSB. I used an aluminum SOPE grade v-block scavenged from work…recycle and reuse 
Setup consisted of first snugging down the bbl to the upper, using an angle plate to align the upper with the FSB and then clamping everything together. I used a Sharpie for indexing marks between the FSB and bbl (alignment check) before cranking everything down. Metalworking is 90% setup, 10% doing. I must have checked my setup 10x!! lol
Here’s a pic of the table. The angle plate is not bolted down…I used it as a “floating” 90* guide, then clamped the upper to the angle plate. A simple bubble level confirmed squareness. The angle plate is heavvvy so it wasn’t moving…it’s purpose was mostly for support.
Good explanation of the process, awesome job. Pin locations looks good to me!
Thank you for your contribution to this forum.
I’ve studied the pictures but I guess I’m confused about what keeps the FSB from rotating when you start the drilling process. I don’t see any other support for it in the photo. Once it’s aligned is the angle plate heavy enough to push the FSB against the vise to keep it centered over the hole? Please explain. Thanks.
Some people will tap the fsb forging on the bottom since there is already hole there from when they drilled the gas passage between the barrel bore and the gas tube bore.
You can tap that 10-32 and hold the fsb in alignment while you do the front pin.
Then, install the front pin and proceed to the rear pin.
I did a few that way before I built a much more solid fsb alignment and drilling fixture.
The barrel is attached to the upper using the barrel nut. I said “snugged” in the above post because it was a dry fit and didn’t want to gall the threads. The top of the upper was indexed to the angle plate keeping everything perpendicular to the quill.
The vise is what really carries all the weight. On one side I used a v-block…it’s actually 1/2 of a mounting bracket once used for an old piece of medical equipment. The other contact point was the bayo lug. The flat surface of the bayo lug pressed directly against the jaw opposite to the v-block. I don’t think I have any good close-up pics of the vice setup but here is a pic of the v-block I scavenged from work.
Not that this has anything to do with the FSB installation but here are some pics of the BCM muzzle comp attachment. Start by indexing the comp then drill a blind hole for placement of the pin…
…finally, Tig weld the pin and blend using a hand file. For some reason there was a small cavity left in the pin after welding. I could go over it with some filler but for now I just stuck it in the blasting cabinet. It looks okay…not great but function over form I suppose.
I think I’ve said it before but that is a NICE jig, AR15 :agree:
– ale
Okay, makes much more sense now. If I do one on this next build I will probably just use the 10-32 screw through the bottom to hold the FSB in place while drilling for the pins. I could build the fixture shown but that’s a lot of work to install one FSB. LOL
Exactly my message, cash. There are many possible setups. This one just happened to work for me with the tools I had available. If I were doing more than a couple I would probably build a jig. I build jigs for Mausers and 1911s because that’s what I like to work on. The AR is just a fun project. I probably won’t do another one of these for a while.
One thing is for certain and that is I will never look at another FBS installation again the same way…E’va!! lol
– ale
I did 4 FSB pinning jobs TODAY alone.
I have done hundreds of them so I have it down to a science…
I could be wrong, but I think he meant that it would be a lot of work to mill a jig as nice as yours to install one fsb, as opposed to it being a lot of work to do the install itself.
I fully understood the same thing.