How big of a problem do you think this is? See the eroded area on the left side. Lack of support for the case head, wonder how much of an issue it is.

Breechface would have to be machined down quite a bit for it to clean up, and then headspace would be too great unless the barrel was reworked to match... right?... and so far, I only know enough to know that would be a can of worms. I guess it could be ground out a bit, welded up and re-machined.

As-is, the gun is more accurate than I. I managed a big ragged hole at 20 or so paces today, so I know it can do it if I can.

Brass tracks

After cleaning

Unless you want match grade accuracy, taking a few thousanths off a breech face is not going to affect headspace enough to cause big worry.

If the pistol is shooting well, don't fix it. The area of the case that's "unsupported" really doesn't need support. The case head is the thickest part of the case, by far. That small amount of the case head wouldn't be an issue. Check your fired cases. Can you see any signs that the case head is conforming to the breech face? Remember, the .45 ACP is a relatively low pressure cartridge as these things go. Were it 9x23mm, with that cartridge's much higher pressures, I'd be more concerned, but it's not.

The issue of support comes into play with regards to the side of the case. For example, if you cut away the barrel clearance ramp far enough, you begin to expose the side of the case above the case web, where the case is relatively thin. That's where it will blow out, to the side.

I see your problem as more aesthetic than functional, so long as the pistol feeds.

Six, that's not bad at all and should be easy to clean up. Strip the slide, take a clean patch, wrap it around an old toothbrush, put a dab of Flitz on it, and with light pressure, move it up and down on the breechface for about a minute or two, just enough to smooth it not polish it.

I polished it a while back. Could use some again I suppose. The messed up area is a few thousandths deep, so it would actually have to be cut to clean up. I'm not too worried about it, it shoots OK and hasn't been a problem. I know with a bolt action rifle going for accuracy it sure would, but with .45 being low pressure like he said, probably no biggie.