Hi, everyone. I was the shooter who had a brush fire break out around his target this morning. For the record, I was shooting .22LR into paper targets on a cardboard back attached to 1x2 wood beams inserted into a steel base. Everyone was confused on how this could have started a brush fire. I have an update.
When I disassembled my target frames and put them into my car, all the 1x2s were intact. When I took them out after getting home, one of the 1x2s had split in two. The outside of the 1x2 looked fine. The area where the break happened looked burned. Pictures are in this thread on Rimfire Central.
The gentleman on the firing line next to me speculated it could have been spalling from the steel he was shooting that started the fire. It appears spalling hit one of my 1x2 support beams, knocking out tiny fragments of wood that acted like kindling, which could light dry grass on fire, but not the entire 1x2.
Update: I take back the burning 1x2 theory. As others in the Rimfire Central thread pointing out, that was likely just a knot in the wood. So I'm back to square one as to how .22LR on paper can start a fire.
There was a report that a shooter next to you shot a red tracer at a target closer than yours, but that impacted in the area of your target. As you noted, there were no indications on or around your target indicating your rimfire caused the incident, which was verified by several of us who went to stomp out the small fire..
While we did ask the line who may have shot the tracer, no-one was forthcoming with details.