David, sorry I didn't pick up on this in my previous post, don't know if you've cracked this one or not, you might be able to overcome this if you set up a screen in front of the chrono's start screen with a hole in it just big enough to shoot thru & get a sight picture, say about 1" wide & 2" high. Wads & cards tend to drop away quick enough to fall below this hole & get stopped before they get to the chrono screens. The sort of plastic corrugated card that realestate signs are made of is good for this & they can be found all over the place for next to nothing.

Steve