Premature finish wear on g42 chamber

[MOT]

The glock 42 barrel here is missing some of the finish around the bottom of the chamber and has a different contour than it’s 9mm bro the 43. This seems odd to me. Anyone know why this is or what could’ve caused it?
The 43, for comparison, has somewhere around 8 thousand rounds through it and has been carried a lot. The 42 has about a thousand and has not been carried nearly as much.
Thanks P&S