I always used silver for lugs, and the fact that I hadn't used brass grated on my nerves a little. The first lug I did with brass, I didn't get full penetration and the filler refused to budge for me after a while. So I cut up some tubes and practiced on them. I made sleeves of 1/2", 1", 1.5" and 3". The smaller ones went fine, but with the bigger sleeves what I found was that my torch wasn't supplying enough heat. After a few tries, I could flow brass through a 3" sleeve, but it was all I could do to keep it hot enough to make that work. That exercise was really useful to me. I got the biggest tip my tanks can handle and it went a lot easier.