I don't know about other people, but I found difference in numerous tests, even when I powder coated at 200 degrees (actual temperature reached 275 degrees F when scanned with IR thermometer). This was mystery alloy, my suspicion it was contaminated with zinc, I did my best to flux it with wax and sawdust and scoop up heavy dross. Bullets dropped at 10.7 BNH average after a week the BHN tested average 14.93 from 4 samples, I discarded 5th sample that was way off. After I powder coated I tested bullets on the 2nd day with avg. BHN 13.1, when tested after 1 week it was same BNH number using 5 samples. So I lost almost 2 BNH points after powder coat. In another example I heat treated WW with 2% tin rifle bullets and end up with average 25.8 from 6 samples. After I powder coated and baked at 250 degrees for 30 min (I was using PID controller so it took about 20 minutes to reach 248 degrees and another 10 minutes to make sure it cured. I placed thermocouple probe in the middle of the tray, the temp never went over more than 1 degree) I tested 3 samples and it was BNH 19.3! Same number on 3 samples. So in this case it was dramatic 6.5 points lost!
I would like to see reports of people what they do, unless they are baking at 450 degrees for a long time like 30 minutes and more, I've tried that, it made my PC brittle, it would come off if I scraped it with a knife.