I have a Colt lower with a Colt safety selector and there is a very definite stop between safe and fire.  It's more pronounced than the lowers I've owned before.  What's the deal?

The colt safety probably has deeper clewaner detent holes than the other safeties .. Some el cheapo no name safeties have almost no detent ...

Bradd_D,

Do you mean there is a definite stop between Fire and Safe or that the stops for Fire and Safe are very firm?

Easy fix:

Pull the selector by  removing the pistol grip and removing the selector spring and detent, or set the selector in between safe and fire and push the selector out with you thumb for the ejection side (the detent pin will stay in the lower receiver and not pop out).

On the selectors detent slot, there will be a Bur/forge line in the middle of the slot (between the two indetent at the ends of the slot and causing the tip of the detent to catch on the bur/line as it passes by).  Polish this bur/line out of the slot and you will have solved/fixed the mystery center stop on the selector.

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If you mean that the stops at safe and fire are very solid, and it seem that you need to apply excess pressure to turn the selector out of theses two positions, then the selector pin tip may be a bit too sharp, and will need to be dulled a bit to allow the detent to ride out of the indetent  of the selector.  

I found if you just run the tip of the detent pin down a file for a few strokes, it resolves the problem by allowing the rear tapered edge of the detent tip to grasp the selector indetents , and not the very end of the tip.

I actually discovered the "burr" last night while I was playing with it.  I tried flattening the point on the detent a bit and it helped a little, but the "burr" has definitely got to go.  I've just got to figure out how to get in there.

Since the selector is hardened, using a Jewelers file isn't going to help.  

Either use lapping-compound with something that is angled the same as the slot, or just break out the dremil with a cutting blade  and go slowly.