The best I can tell I made the first post here on the Cast Boolets site about using silicone baking mats instead of foil, parchment or whatever to cook Powder Coated bullets. I also told all this was not my idea! It was my wife's idea because she got tired of looking for the non-stick foil in my garage. So she presented me with my first package purchased from Costco and those same mats are still being used.
Why do I use silicone mats? Because they are a one time purchase or at least have been since I got into PC in 2012. I don't have to be continually purchasing foil or parchment. The bullets don't stick to the silicone and the mats will withstand 500+ F. degree temp. The mats are heavier, lay perfectly flat and do not tend to slide when placed on a flat surface.
When the PC bullets are placed base down the powder tends to fill in casting imperfections on the base. Since imperfections on a bullet's base cause inaccuracy at least in theory the bullet's base is improved. When a tray is loaded the bullets do not tend to slide on the silicone like they do on slick foil or parchment, making it somewhat easier to transport the tray to the oven.
However, after one cook or hundreds of cooks, the mats do show signs of use mainly due to spots of powder buildup, etc. but the mats are easy and simple to clean. When I first used the mats I realized there were spots of powder that were bonded to the mats like glue, but I also noticed where the bullets were cooked and removed the mat was left pristine. So i thought why not try coating the entire mat with powder, cook it and see if I just ruined a mat or not. What I found is you simply peel off the layer of cooked powder and it leaves a clean mat.
If I am cleaning several mats I spray the mats with powder. if I am doing just one mat I shake powder in a fine sieve to put on a thin layer of powder. A paint brush, like I use to sweep up powder overspray, can be dipped in powder and dobbed on a mat to deposit a layer of powder. Cleaning my mats is one of the ways I use powder sweepings or some unused powder from Harbor Freight that I purchased and didn't like after trying it.
I did one half of this mat in the photo to show a before and after.