I am in the middle of a 9mm AR (colt) build and and it seems the bolt is not compatible with the lower receiver. I guess this is what happens when things get strung out over 10 years.

Anyways, it was suggested that I dremel the winds on the outside of the feed ramp. to make the bolt slide over the feed ramp sides. While I do have a dremel, I don't like the idea of using it in this situation and think maybe a file would be the better option. Should I use a dremel or a file? If a dremel, what tip would be best? If a file, what type of file? I have some files I bought at Home Depot, but not sure if those would be the correct files.

Is there something I could put on face of the bolt or feed ramp to help mark how much material, and what angle to be taken off? I was going to put some chalk on the bolt and hope if some would rub off on the feed ramp to help mark mark it, but is there something better I should use?

Should I use a blueing pen or something over the area to file for corrosion protection afterwards?

whichever way you decide to , remember that it takes a lot longer to fuck up with a file.

File, slowly once you get some metal exposed use a magic marker to paint it and see where you are hitting.

I would consider a sanding block, you can move a lot of aluminum with a coarse paper and it won’t clog like a file, then finish with fine paper.

Chalk your file to reduce clogging.

My rule:

A dremel for cutting (destruction)
A file/stone for fitting

Dremels are probably responsible for as many, or more, destroyed firearms as our own worthless government. In for the post dremel destruction and accompanying tears......

Dremels are very good at screwing things u in the blink of an eye.

The power is far better limited by the shaft system on a Foredom tool.

Dremels encourage excessive speed to try and maintain control that destroys things in the blink of an eye.

As the others have said, it’s much easier to cut flat & straight with a file than a dremel.