When I first started using my Chrony, I found that gas checks were coming off and hitting the Chrony. Sometimes they would hit the 1/8 inch wood dowels that I was using on cloudy days to mark the sides of the bullet paths and cut the dowels right off. This was unacceptable.
I went to the local glass shop. The place that fixes glass in storm doors and suchlike. I bummed some scraps of quarter-inch LEXAN sheet. It has to be LEXAN, which is the stuff that 'bulletproof' "glass" is made of. I made a piece that was big enough to cover the machinery part of the Chrony and used a couple pieces of coathanger wire to hook it over the front of the Chrony. The gas checks make nice round imprints in the LEXAN but no damage to the Chrony has occurred since. Sometimes I still lose a dowel, but they're cheap and easy to find - any hardware store has them. I get an average of 1 hit on the LEXAN from every hundred shots or so.
Best regards
John