I tried to find it again in the FAQ and re-read the shim link and in a site wide search for "Silver Solder" and came up with nothing. I remember seeing some stuff from you about Radio Shack, but cannot locate it. 8( Sorry, not trying to give bad info, this was just the Silver solder I came up with on a quick websearch.
I think we wasted more space telling him where to find it. There are several ways to join metal. Most people are familiar with welding,which actually melts the base metal of the two parts together and adds a little filler metal to make a good joint. This can be done by several processes. TIG uses an electric arc from a tungsten electrode with a "sheilding gas" which is usually an inert gas like helium or argon,but can be CO2 or Nitrogen depending on what your welding. Filler metal is usually added from a metal rod. MIG uses a similar shielding gas but the electrode is a wire which is fed off a spool,which is also the filler metal. Sheilded Metal Arc welding is also called stick welding. Thats what most of those cheap arc welding machines are. The electrode is a metal rod coated with flux. The flux melts and vaporizes and keeps your joint from contact with the oxygen in the air. When your done there is a hard coating of slag over the joint that needs to be chipped off with a hammer or pneumatic scaling tool.
Oxy-fuel welding does not use electricity but instead uses gas tanks. Oxy-acetylene is the most common but oxy-propane and oxy-mapp gas welding is also done. Often this type of setup is used with a different handle and or tip for cutting as well. When your cutting,you use a flame with alot of extra oxygen. The flame heats the metal to the point that it will burn with the excess oxygen creating even more heat which is enough to burn and melt through the metal. When welding you adjust the flame to consume all the oxygen. When welding some metals,these gasses,which have little or no oxygen will work like the shielding gas in a TIG welder to protect the joint from the affects of oxygen in the air. On other metals you need to use a flux applied to the join which floats on top of the pool of molten metal and keeps oxygen away from it as well as dissolving any oxides on the surface of the metal. The worst offenders are metals whose oxides melt at a much higher temperature than the metal itself. Aluminum is hard to solder even with the correct solders becuase it has a low melting temperature and the oxides on its surface are alumina,which is the same material as sapphire and has a melting point of over 2000C (compared to around 660C for aluminum.) This also poses problems with welding aluminum (aluminum also has the problem that it conducts heat really well and the low melting temperature gives you little margin for error) and there are various methods developed to get around it. It can be soldered and welded,but its tricky and has to be done right or you end up with a ruined part or just a puddle of molten metal.
Soldering and brazing are really very similar. The parts are heated and a metal that wets and sticks to the surfaces of the parts is added. This should be contrasted to welding where the metal of the parts are actually melted. Often a flux is necessary to dissolve and clean the oxide deposited on the surfaces of the metal that's being joined. These oxides often form in air,but heating makes it even worse. Soft soldering is typically said to be soldering with those fillers that melt below 400C. Its not really a statement about the strength of the filler although often the strength and working temperature go together. Lead based alloyed are commonly used for this although lead free alloys with low melting temperatures are becoming more common and in some applications,such as water pipes are required in most places. Brazing is similar to soldering but at higher temperatures. Brass filler is one of the most common materials. Brazing rods made from brass,often coated with a solid (at room temperature) white flux are commonly available in hardware stores.
Silver soldering is a term that is very confusing and sources will argue as to its meaning. I was taught that the correct usage was for a silver based solder with a melting temperature above 400C. I was taught that it was synonymous with "hard soldering" and sometimes "silver brazing",especially outside the US. The only difference between silver soldering and brazing is that a silver based alloy is used. The only difference between soldering and brazing is the temperature.
Where it gets confusing is that there are many low temperature (often lead free,but sometimes its alloyed with lead) alloys that are used for soft soldering that contain silver. These are often called or marketed as "silver solder". Therefore when someone refers to silver solder,its often hard to figure out what they mean.
On thing to remember about the strength of all these techniques is that it depends on it being done CORRECTLY. With welding sometimes you just butt the peices up together and the weld can penetrate all the way through,in other cases you grind a v shape at the joint so you can get the weld started deep down and fill it up to the surface as you work. With brazing and soldering you need a thin gap for the solder to flow in through capillary action. Depending on the properties of the solder this will be a few thousandth of an inch. (silver soldering/brazing works like this and is very strong,so long as the gap is not excessive. Thats why peoples silver soldering jobs fail so often) Often I have heard people recommending a v when silver soldering or brazing. They have even argued "I like to do it that way so I can make sure it gets down in there" With silver solder that is wrong and weakens the joint.
Thats why people will tell you that you cant silver solder in a bolt handle. You cant chop it off with a hacksaw,file it flat and expect it to work as your gap is going to be in the hundredths of an inch (or even 10ths) If you had two machined surfaces,it should work fine.(in fact,if your smart,you would machine a hole and put a pin in,then silver solder it all together. Of course if you know how to do that and have the equipment,you probability have TIG welder in the corner of the shop too,which would work great. In other words,silver soldering takes as much skill and effort as welding. Its not a shortcut where you can just glob it on and fill over that crude hacksaw job and then file it down with a dremel tool so you can hide it all.
Soft soldering is often appropriate when you dont want to ruin the properties of the metal your working on. All soft solders (or filler metals in general) and not equal in strength or other properties. Some have much higher strengths than others. For some applications you would want to use these low temperature alloys as if you heated the metal to the point it was glowing,you would ruin the part. (Imagine taking your shotgun,heating it with mapp gas until it was glowing bring red,brazing on a scope mount,cooling it down and then taking it out to the range and shooting it. Not only will the finish be ruined,it will probably explode.)
As for where to get the right solders and fluxes,if would try your local Airgas or Praxair dealers,but if they dont have them you will need to order them from Brownels. If you dont know what your doing,practice on some scrap steel until you get it perfect before you actually do it.
If I have made any mistakes here,someone come along and correct me. Its been about 12 years since I had to take that metal shop class as an undergrad so I may have missed something or gotten it jumbled around since some of these things I have not really used since I learned them.
