I read somewhere that they approved lightning strike welds, if one was so inclined to go climb a tree in a thunderstorm and wave the barrel around...
But the fine print, if I remember correctly, is the lightning strike weld must cover at least half of the area where the 2 parts meet. So not only do you have to climb a tree and wave the barrel around, you should be somehow spinning around in the tree to get the proper coverage during the strike.