I use 60/40 and a paste flux.
Simple no-corrode that washes clear with hot soapy water.
If I do use an acid flux,,it's only for tinning so it can be washed from the surfaces before assembly. Never used for final assembly.
I have use the Force44 tin/silver stuff. It works, works well, but I don't really see any advantage. It needs a little higher temp to work at and I don't care for the forever bright silver line it leaves along a joint.
Lead/tin solder oxidizes to a dull grey with some time and blends in much better. Not an excuse to use solder as a putty filler of sorts though!
Parts must fit together well before hand.
I tin the ribs and most of the bbl surface with a electric soldering gun (WEN pistol grip type, nothing fancy).
Surprising how much of the bbls you can do with one and how quickly.
Ribs are especially easy to over heat while tinning them with a torch,,even a propane. No chance with the 'gun'.
From about the forend lug back to the breech, the bbl mass is too great for the small soldering gun, so I finish that up with the use of an acetylene torch.
I use acetylene here only because I like to be able to take advantage of it's heat potential,,not that a propane won't work, and work just as well. You have to be awfully careful w/acetylene that you don't overheat things.
After the tinning, check it again to make sure it's a nice, thin, smooth coating. Remove any excess lumps and bumps.
I clamp things together w/ a pile of small C clamps and use lengths of rod along the ribs. A few clamps cross wise on the bbls to prevent separation too.
You should have (3) spacers soft soldered in between the tubes along their length also.
(Though I did have one with what appeared to be pieces of popcycle sticks, Never did figure out how they put that together w/o burning them.
They sure did when I went to remove the loose ribs!)
I use clamps,,some use the twisted wire method to secure the new work. What ever works.
I'd been a failure with the wire thing so I started and continue to use the clamps.
I solder everything up when it's set to go using a propane torch. I start at the breech.
Making sure the top rib is set corectly against the short section that's brazed in place.
If you start from the muzzle you can find yourself with an expanded and lengthened rib that's a bit too long to mate nicely with that section at the breech.
Gently tighten the clamps as necessary as you go. Watching the solder melt and flow along the joints and if necessary add a touch of solder.
Hammer flatten the solder wire before starting. It makes for easier access to the joints and the thin profile melts quicker when touched to the steel. Gives just enough. Any excess is just more cleanup work afterwards.
A full length burner sounds nice but I don't know how you'd control the thin portions of the bbl from getting too hot and possibly overheating before the breech section.
Having a full 30" long 400F bbl assembly of several parts clamped or wired together isn't what I'd want to wrestle with.
A temp controled oven of some sort would work, but then there's no easy way to man handle the rigging if you need to adjust the clamping fixtures, add solder, ect.
Take it slow and easy and it works just fine. The entire bbl set doesn't have to fuse at the same moment to make a good soldered joint.
In a factory setting, perhaps that would make for a more time efficient ($$) manner.
But I don't think that's what we're after here. Certainly not what's on my mind when I put one back together.
Simple tools and sound, basic soldering techniques have been the way for a long time.
