I just got a new AR upper receiver to build my MK18 clone and it has a X forge mark. I did a search but couldn't find out who the forger is. Any idea who it is?

Also I need to pin my 14.5" Vltor 5C1 FH on another build but not sure what to use as a pin. Any ideas on what to use for the pin for the pin and weld?

Thanks guys!

I've not seen an "X" used as a forge mark to date, so no help there.

(I'd be interested in a pic though. )

As for the pin,  ATF does not specify pin material to be used. Some use a section of coat hanger wire, other a drill bit shank, or finishing nail shank. I use 17-4 SS pins, we stock them at work (easy button) and they melt nicely when using a Tig to P/W.