Years ago I bought an unusual little MM cob in an antique store that had a removable vulcanite stem, and no shank. It had been used before but I cleaned it best I could and loaded it with Prince Albert. It didn't take long before I noticed it was starting to burn out on the bottom. I figured it was mainly because the stem didn't go into the bowl like the usual cobs, but just went into the bowl a short ways above the bottom. I ended up putting a little super glue on the label on the bottom, and then filled the inside of the bowl bottom with a good amount of pipe mud. Smokes just fine now, but I'm not sure I'd do it to an ordinary MM cob, unless I really liked it.