444 Marlin. Odd gouges in chamber - failure to eject - brass marks.

[Spyder]

That seems to be the consensus. Thanks everyone.

I ordered that barrel from Numrich. Now, to find a local smith in the north SF bay area that can do good work...

[rromeo]

Just out of general curiosity, is your barrel stamped New Haven CT or North Haven? I'm a bit of a Marlin nerd. They moved factories between 1969 and 1970.

[Spyder]

Had to look, it's North Haven.

Now I'm curious what the new incorrect barrel will be! The ad says "all original markings intact" or something similar, so hopefully it's stamped correctly and has the JM stamp too. This one, the JM is on the right side. I'm pretty sure all my others are on the left.

[slamfire1]

I would say a chip of something got on the reamer during manufacture, created a gouge, and yet the rifle went bang and was shipped.

I don't see anything solution other than a new barrel.

[rromeo]

The new barrel will most definitely be North Haven. They moved from New Haven to North Haven 1969-1970. So some 1970 guns still had the older barrels.
Bad news, if it is in fact a brand new barrel, it will not have a JM stamp. Those were proof marks, so the barrel was stamped after the rifle was complete and test fired. As a big Marlin collector, I don't actually care about JM stamps. I know where the guns were built from the serial number, and rollmarks, so the proof mark isn't a big deal to me.
1970 was also around the time the stamp moved to the left side of the barrel. There's no significance on which side.