A few years ago, at a rendezvous in Ft. McMurray Alberta, someone shooting a too thin patch started a forest fire. It was discovered by nearby shooters on the line, and an attempt was made to stamp it out, but it got away from us. Picture seventy-five shooters who have dumped their rifles and gear on the trail and are frantically stamping the bush. The fire jumped the trail into the bush on the opposite side of the trail, and finally a fire wagon from the club arrived and got busy. It took nearly an hour of panic to extinguish the fire(s) and all of the suppressant in the trailer. We had it nearly beaten before a helicopter arrived to assess the fire. By then, if we hadn't got the upper hand, we might all have been lost in that fire.
Cause, someone who was using a thin cotton patch that ignited upon firing his rifle. And as Daryl has pointed out, we've seen it in the grass at the BC Rendezvous as well. Yes, a smoldering patch can ignite a fire.