Passes headspace check but....

I have a 1903 with ser. # 14175XX that has a 8-32 barrel on it. If I'm not mistaken that is the original barrel. It does not close on a No- Go gauge. But the problem is it's a total sewer pipe. No lands and grooves. Dark and rusted/pitted bore. Crown is not all banged up. Has a TE of 10.0+ on my gauge and MW of 5.0+ . Is this possible? (I guess anything is ) I'm thinking someone shot corrosive ammo out of this thing and never cleaned it. I do have a replacement barrel, RA 5-42, that will go on it to make this my shooter. Any thoughts?

Does it look leaded? the gauge reading would indicate that shooting it might be a bad idea. Corrosive ammo might be a cause of corrosion and pitting, but not enough to erode the barrel completely. I would rebarrel like you plan to and then shoot it till it needs another barrel.

headspace and barrel wear are 2 different issues...time for a new barrel..

When I brought it home I ran a few patches through it and out comes what looked like metal, corrosion, fouling. The more patches the cleaner it got but the less the rifling was visible. At that point I knew it was toast. IIRC I paid under 300 for the rifle. Plus 120.00 for a replacement barrel. I have a RA 5-42 for it. Still a bargain for a shooter in my book. I am curios how the throat is gone as well as all the rifling but still headspaces??

Headspace is from a spot on the shoulder of a bottleneck case to face of bolt. Has nothing to do with throat or rifling . You could cut the bbl off through the case neck area and still check headspace.
Chris