what torch/tip? I think experienced framebuilders are separated into two camps: some like to use exactly the right tip for the job, and others like to use the biggest tip they can get away with.

My experience with brass was that with the practice tubing I could use a moderate size tip for rings about 1" in length. But when I tried 3" long rings, I didn't have enough heat. I did manage to trick the brass into penetrating the full length of the sleeve, but it was a travail, and I got a lot of carbon precipitating out on the surface of the sleeve. So I got the biggest tip my tanks could support, and it was a piece of cake. You need approximately 7 times that volume of acetylene than the tip will flow or you start to burn acetone, which is bad news. For my Smith AW1A, I ended up with the AW207.

I haven't tried a lug with brass yet. When I get ready to build a bike that way I'll probably do some more practicing. The real utility of the sleeves for me is on fillet brazed frames at the seat joint