Scrap lead pipe is pure lead. Very soft, and usefull only for blackpowder bullets.
Just smelt it down in a large cast iron pot and skim off the residue and crap that floats to the surface. Be careful not to put the pipe pieces directly into the melt...they may contain water and spatter molten lead all over! Preheat pieces first near the heat source, and get them hot enough to drive off any remaining moisture.
50-50 solder is half tin, and what I use to alloy the pure lead with. If you have access to wheel weights, mix that about 50-50 with the pure lead for general purpose pistol and rifle bullets. Increase the tin content to help the mix flow better.