I never use acid flux, It does work great but I've too often seen the result of it not being completely removed from the surfaces.
It's not needed IMO as long as you clean everything before you start soldering and don't burn the regular flux.
I use 50/50 or 60/40 ,what ever I seem to have at hand.
I've used the Tin/Silver 95/5 stuff and it works OK. But I don't see any real advantage to it plus I don't care for the solder line always remaining a brite white color.
At least the lead/tin stuff does oxidize and turn dark grey after a time.
Flux is the paste in a plastic jar from Home Depot sold for plumbing work. No-Corode was the older catch all name for the stuff.
I use a 200w hand held soldering 'gun' to tin the ribs and then also tin the bbls as well. The 'gun' has enough heat to easily tin the bbls all the way untill you get just past the forend hook. Then the
wall thickness starts to work against you. A smaller watt unit won't have the power to tin the bbls but will work on the ribs OK.
From there I use a propane torch with a 'pencil flame' to heat the surfaces and tin that last little way.
After tinning I go back over the surfaces of both the bbls and the ribs and smooth them to remove any lumps or bumps of solder. A coarse file run over the tinned surfaces takes care of that quickly.
This so the ribs lay down nice and flat when first clamped up for sweat soldering.
I recoat the tinned surfaces on both the ribs and the bbls with flux once again.
I lay the tinned ribs in place. I use a length of 1/8" square steel 'rod' on top of both the upper and lower ribs. Then a bunch of small C=clamps placed every 3 to 4 inches or so gently tightened down pull the ribs down onto the bbl surfaces.
All clamped up, check the rib for straightness and no canting at the muzzle end.
Then begin sweat solding it down into position. I use the propane torch for the soldering.
Begin at the breech end,,always..
The rib will 'grow' due to being heated. If you start at the muzzle, the rib can expand in length just enough to be too long to match up with the solid portion of the top rib at the breech.
If during the process you need an extra clamp when you are soldering,,take one from the opposite end of the assembly where you already soldered things up. . That'll be set already,,Still Hot!,,but solidified.
I use scrapers instead of files to remove excess solder from the surfaces. Much like wood inletting scrapers/tools, they can be used in a pull fashion and remove the soft solder efficiently and smoothly. You get a feel for how much pressure to apply and at what angle to hold the edge so that when you get to the surface of the bbl steel, it will scrape very smoothly and not leave chatter or gouge marks. Saves a lot of clean up time.,,and no clogged up files with solder.
A 'V' pointed tool gets right down into the rib joint and cleans out the solder and can also scrape the steel clean at the same time.
