@FREEFALLE7
Hi,
Spot checked some Colts in my collection...
One lower has similar vertical sunken indentation across the roll mark.
Several of my older LE-prefix lowers have the same/similar markings on the inside of the magwell.
My educated guess is that they use some jig or fixture to support the magwell from the inside when the roll mark gets applied to the lower.
What you are seeing on the inside is a side effect of this... The jig probably doesn't cover the whole interior - leaving a small section by the machined ridge unsupported,
and some of the aluminum getting moved during the process.
I checked a newer Colt lower that is engraved (ie. not roll marked), and the inside of the magwell is perfect/flawless.
So... Unless you are having issues with magazines not dropping free, I wouldn't worry about it! IMO, it is normal for Colt lowers that have traditional/old-school roll marks.
thanks,
jjk