sJ22, please give more detail as to how you are collecting the shot. I know you said you drilled a hole..... So your magnet never actually comes into contact with the metal trough; correct?
Drilled hole in bottom of trough and put a stick in it while shooting and then a bowl under hole and raked the shot in it, didn’t think about a magnet or I would have used wood trough. The way I do it you have to rinse away all the carpet debris