I remember going through something similar. The Krylon Rust Tough Semi-Flat (which is good paint) is much flatter than Dupli-Color Semi Flat Black. If I recall, I would say the Krylon is about 40% gloss, the Duplicolor is 60%. I made the mistake once of spraying about 5 brackets with Dupli-Color, then one bracket with Krylon (after I ran two cans of Dupli-Color dry), and they didn't match.

So I wouldn't forget this in the future, I took a few thin sheets of aluminum and cut them into squares about 2" x 2", sprayed them with literally all of the various spray cans I have on my shelf, then taped each piece onto the appropriate cap. I got tired of always guessing the differences between flat, semi-flat, semi-gloss, and gloss between the manufacturers.