Odd Browning hi-power barrel

[hdm25]

I recently purchased a LNIB Browning hi-power Mark III. I picked it up at an EXCELLENT price and have no real regrets BUT, when I thoroughly inspected it, I found something with the barrel that I had not seen before and am wondering if anyone can tell me anything about it. The barrel has a small cut-out on it right about where the end of the extractor is. It looks like something from the factory but I can't figure it out. I am wondering if it is something from the factory that I have not seen before or if it was done by the previous owner. If I have to rebarrel it, I am not that concerned as it will make the total price paid for the gun come out to be about what I would expect the gun to cost, anyway, but I would rather not do so. I have not yet fired it and won't have the time for a few days, so I don't know if it impairs the functioning of the gun or not. Anyone have any ideas? I have owned at least four Mark III Brownings and numerous surplus hi-powers and have not encountered this on any of them, though I seem to recall seeing it on a used gun in a gun shop a while back. This might actually be the same gun...I'm not sure. Any information would be appreciated.