I live around the block from DavesMetalWorks and happend to get one of the first one peice tubes made, and He told me that it is made of steel. He is currenty working on some aluminum tubes for the lower half of the extention tube for the old M1super90s that people removed with pipe wrenches. Also on the work bench is some aluminum tubes for the Mossberg semi-auto and the Winchester X3
I personaly preffer steel and will say that I would like a one peice machined tube IonBonded or Melonite koted. Instead of a blued tube with a welded collar to stop the threads that moisture could possibly collect in and rust, BUT I will say for the amount of hiking and shooting I do with my M4 the DavesMetalWorks tube has not shown any signs of weakness and is by far exceeds the quality I would expect from a 60-80 dollar magizine tube and thank the lord its not ATI LOL