Sounds like a ringed bore to me too.
Can happen when firing a round with a bullet already stuck in the bore,,or even a cleaning patch or other obstruction.
It bulges the bbl causing the ring in the bore. On most .22rf rifles w/a bbl of any substance the outside damage is barely noticeable.
Many times the surface only shows a uniform width line all the way around of the metal being stretched. That could be what you are seeing and taking as a weld line.
You can usually feel it when you slide your finger over it, but it's not much of a bump in the surface on 22 rifles generally.
Thin bbls on 22's like handguns and bbls on centerfire rifles & shotguns usually show a much more pronounced bulge on the outside as well as the ring inside. The centerfire rifles having much more psi,,the shotguns much thinner bbl walls.
I can't think of any reason why the Winchester factory would ever repair a bbl by welding sections together like that. Just wouldn't make $$ sense and with safety in mind,,they proof fire every bbl and bbled action before it left the factory. One with a ring in it wouldn't have left NewHaven.
A bbl ordered as a separate replacement part would have been proof tested also on a test recv'r at the factory and have the so called 'Postal Proof' mark on it of a 'P in an oval' instead of the standard finished arm proof mark of 'WP in an oval'.
If it's working OK for you, I'd leave it as is.
You could have the bore relined which would remove the ring inside and give you a new bore and chamber.
The outside would (could) then be struck and refinished to remove the damage on the outer surface. Properly done it can be un-noticeable from original.
Not properly done it's just a refinished bbl on a Win 22 pump. That'd lower the value,,but so does a ringed bore,,so take your pick.
The other option is to look around for a orig Win replacement bbl w/a nice bore and switch them. They are out there.
There are also new mfg replacement bbls complete w/ Winchester roll marks on them. Not cheap either.,
I think there are 4 or 5 different bbl address markings for these Mod 61's alone plus they were made in both round and oct, and single caliber only as well as short/long/lr.
Just some thoughts if not confusing ones..