I am at a loss for an explanation. I am not a machinist, but it seems to me, removing metal from the front of the barrel lug, would make the barrel move forward, and increase the head space, not shorten it. Why does anyone do the strange things to perfectly good guns? I purchased a Model 52 Winchester,”International” model from an estate years ago. For those of you who are not familiar with this model, it is the top of the line of Winchester bolt action .22’s. Someone had drilled a hole in the forearm tip, just under the barrel and inserted a 3/8 inch threaded rod and had various nuts screwed on to it, for balance purposes, I suppose. Anyway, back to your barrel, I would think a temporary fix would be to put a shim in the curve of the lug to move it to the rear. A permanent fix might be to weld up part of the curve with a Heli arc welder, and recut. Hopefully, someone else will have an idea.