Just got a 14.5 inch threaded AR barrel.  That's what they had in stock ready to ship.

My neighbor is a welder with welding equipment.  I have a nice big drill press.  I have a Phantom FH.

Now what the hell do I do to pin and weld the Phantom to my barrel????

The first thing I do is determine where the bottom of the FH will be.  If you have a Phantom that needs to be indexed (closed bottom), it is easy to determine the bottom, but you you have the fully open type, test fit the Phantom to the barrel and find and mark where the bottom is.

Next measure the thickness of the Phantom at the marked bottom.  This will determine the length of the roll pin you need to pin the FH.  Add 1/16-1/8" to your measured length to compensate for the amount the pin must engage the barrel.




Next, drill the proper sized hole at the marked bottom of the FH.  Install the FH and tighten to whatever spec you prefer.  Then you need to drill the barrel 1/16-1/8" deep into the threads.  I use the same drill bit used to drill the FH, insert it into the hole of the FH and mark it with tape 1/16-1/8" higher than flush with the FH.  Drill the barrel until the tape touches the FH.  Drive in the roll pin and clean it up flush if it isn't already there.



Now it's ready for welding.  I use TIG.  I strike my arc directly over the hole and get the pin and surrounding metal molten and add a little filler rod and it comes out nearly flush with minimal cleanup required.  Repark or recoat with whatever you like to use.



I've also done this with setscrews using the same basic method described above.  The following poor pic is a Vortex set in place with a cone tipped setscrew prior to final weld.

Great!!  Thanks mongo001!

Now I know what and where to pin and weld!  I really appreciated all the trouble you went through to post those pictures.  

What do I owe you?  

Quoted: What do I owe you?

If we ever meet, a beer would do nicely.

You got it!!

Thanks for the info, Mongo.  Where did you get the setscrews?  Are they 4/40, 6/32, or 8/32 thread?

I hope someone saves mongo001's post.  It would be really nice the next time someone asks, "How do I pin my f/s?".      

Hey....I asked too.

Thanks a bunch mongo001!

Quoted: Mongo, where did you get that mongo set of rollpins

I got this HUGE lot of misc parts, most of which were AR parts, but some of them, including the roll pin assortment, weren't AR specific, but come in handy all the time.

Quoted: Thanks for the info, Mongo.  Where did you get the setscrews?  Are they 4/40, 6/32, or 8/32 thread?

Missed this one on my last reply:  Generally I use 8/32 with the cone tip for better grip.  The cone tip fits nice and secure into the drill dimple in the barrel threads.  Once welded over, it will not come off.

One side not on that project:  The Vortex G6 seemed to be hardened all the way through.  It was laughing at drill bits and the hole had to be made on a mill using an end mill, but that made for a perfectly straight and true hole, so it is the most correct way to go anyway.

Great writeup Mongo!