I think the instructions say not to use fiber wads in it, but I have no idea why, it words fine for me with them.
With fiber wads and some of the older smokeless powders you had to put a very heavy wads pressure on the (up to 100 pounds) to get a clean burn. The press is not capable of that kind of pressure. Red Dot and fiber wads used to have a reputation for bloopers with worn cases or not enough pressure, Green Dot is said to have been created to over come this problem.
Herco is another one that required a heavy wad pressure and I'm sure there are others. I've got some of this information in old books I haven't unpacked yet.
No worries with black though.