In the 1950s, when these M1s were originally found to be overly worn and demilled by torching them in half, most of the barrels were shot-out too. The guys who bought all this surplus "steel" needed a source for barrels to put on the receivers they welded together.

At that time, Springfield '03-A3 barrels could be bought new for less than $3.00 per barrel. Since these guys seem to have had much more time than money, they "built" new 2-groove barrels like the one you described. Interesting to note that the '03-A3 barrels were silver-soldered to the garand chamber stubs they had drilled out.

What's amazing is that aside from some cracked receivers, most of this cobbled together junk (that was never re-heat treated after welding) has not failed and is still functional today, although I personally would not risk shooting one.

BTW- no one actually knows how many welded M1s are out there. Obviously thousands. I have sure seen quite a few, at least a hundred or more over the years. They just keep turning up, and most have the wierd, stubbed 2-groove barrel.