Miller, as for the metalurgy of the barrels, a while back I went to a scrap yard and bought some aluminum round stock from 3/4"-15/16" cut to 8' long. I wanted 6061 as this machines rather nicely. A fellow came out and put a hand held machine on it and in a few moments it read what the content was and it was determined it was 6061. I would venture to say barrel steel could also be done and will have to ask them.

Chuck, with this being such a small weld, if the area was pre-heated and then welded, I don't think there would be much metal cracking, but like you stated, dye check anyway.
Also if the area did air harden, filing it will tell.

David