www.silversupplies.com/catalog/metals/silver_solder/paste.shtmlKitchen vinegar is going to be the solvent that you use to remove the parkerizing from the barrel and FS thread. Just don't allow the vinegar to sit where you don't want to remove the parkerizing.
Once both threads have been stripped down to bare metal, take a dremel and slot down the barrel thread on the top and the bottom. This will allow the Silver solder a place to thicken up more than just threads to threads.
Now apply Silver solder to the threads, index the FS, then coat the barrel just below the thread line with insulating paste. The insulating paste will keep the heat from transferring down the barrel, and keep the silver solder from wicking down the barrel as well.
At this point, light up the FS with the Mapp torch until the FS becomes a dull red (Not bright red, and the past will start to flow before the FS is dull red, but you need the FS that dull red color to make sure that the barrel underneath has gotten hot enough to allow the solder to bond to it as well.
Once you entire FS is dull red, remove the heat and allow the FS to cool.
Once the FS has cooled down, hit the FS with Cold bluing (cold black). This will recolor the FS to the Black to match the parkerizing on the barrel.
From there, wash off the insulating paste and to neutralize the cold bluing, then lube the parts with CLP to give them a protective coating to the parts to prevent rusting.