As stated by Mark above complete tinning of the barrels and the top/bottom rib is of utmost importance. I am going to share with you one of the "secrets" of the gun trade in how to make sure that the tinning is absolutely complete prior to the soldering of the ribs to the barrels. The use of a product commonly called "tinning butter" used by the old masters of the auto body repair prior using lead (prior to plastic body filler) is the secret. Tinning butter is available in different combination of lead and acid and even 100% tin and acid. Using it on barrels and ribs THE ACID RESIDUE MUST BE WASHED 100% AWAY AND NEUTRALIZED WITH BAKING SODA AND WATER and you need to do this several times prior to relaying the ribs to the barrels using lead/tin solder and pine rosin flux. I purchase pine rosin from Diamond Forest Products in Georgia http://www.diamondgforestproducts.com/~shop/rosin/1-lb-powdered-pine-gum-rosin/186879/

I use tinning butter "Tin EZY' from Johnson Mfg Co. in Princeton, Iowa ---telephone them and they will ship it to you---- http://www.johnsonmfg.com/temp/tinning.htm

Do not use acid tinning butter for spot the repair of ribs. The ribs must be completely removed in using tinning butter as all acid MUST BE REMOVED before using traditional solder and pine rosin flux.

Here is a video of a master auto body craftsman using tinning butter so that you can see how it is applied