I have missed a good number of silver halves rimchecking, but will never do anything but. I have caught them when I drop them in to the canvas bag I used for the dump. I let the coins kinda cascade out of my hand so I have a chance to notice a glimmer of silver and when they fall into the bag, you can not miss it when you hear the sound of silver. The more I searched, the better I got at spotting those hidden silvers, I can easily spot the copper edge/dirt silver since usually there is still silver showing, its just not as pronounced and its would be on the outer edge of the cooper.