So far, I have soldered underlugs on only one barrel and it worked fine. I used the low temp solder TOTW sells. One tip, and I learned this the hard way, is that when heating the underlug to tin it, apply the heat slowly with as small a flame as possible. At first, I was overheating the underlug which burned off the flux so the solder wouldn't flow and adhere to the metal. Once I figured this out, it was surprisingly easy to solder the underlugs.