Normal wear for 3k, being that every time the carrier comes back, the bottom of the carrier has to over cock the hammer so the disco can catch it if you have the trigger held back.

As for why the side of the carrier bottom and not the center for the wear marks, best guess, the hammer  pin channel was not drilled perfectly square with the hammer itself,  the hammer channel in the receiver not perfect, or even just the top of hammer contact pad not perfectly square to the pin line.  
Does any of this matter, not the least, so stop worrying about it, and chalk it up as just normal bearing wear marks on the parts.

If you have a Colt open bottom semi carrier, then chances are is due to you having a Colt receiver with a sear block installed.
Hence standard carrier will not work in the lower, since they will not clear the sear block.



If you don't have the colt sear block, then the rig can use any carrier,


Hence the new colt bridged lower will work with any carrier as well.

New colt bridged lower, that replaced the older lower with the sear blocks.

Ditto, since you will end up horning through the harden surface of the hammer contact pad, and will end with the softer metal of the contact pad  just peening instead.


And to add, if you are trying to square the hammer contact pad with the carrier, then you have to first jig up the hammer on the pin channel and not the sides of the hammer.  Next comes trying to flush the surface of the contact pad, and that takes a flywheel cutter with a carbine cutter since you will just wear out a HSS cutter since the hammer surface is just as hard.   And the fun part, once you are done with that, would need to first reheat treat the hammer, then temper the steel afterward so the hammer does not shatter instead.

So bottom line, leave the hammer/rig alone and just shoot the dam thing instead.   The hammer and rest of the parts are serviceable items, and in say 20K+ when you wear out either the hammer sears, then you can replace it then

Before you order a new FCG, measure the trigger and pin sizes so you order the correct size parts!!!!!

Colt used to use a over size  pin fire control group with the pins and channels on the parts of .171, instead of standard 154" mil spec size instead. (part of then not wanting there semi's turning to full autos; like the sear blocks.  

If the lower receiver channels for the .171" pins, then you will need to order a .171" fire control group.  

If you try to use a .154 FCG in a  receiver set up for .171" parts, the pins will be too small for the receiver channels and the slop of the pins in the  receiver channel will cause nothing by problems with the FCG not working correctly (same goes for trying to use .171" parts on 154" pins).