There is no need for such tests, Utah state fire marshal Brent Halladay said. With steel bullets, "you might as well just go up there and strike a match," he said.
Statistics on wildfires caused by firearms are incomplete because the federal government does not list "shooting" as a cause on its fire reports. But some officials write in "target" or "shoot" as a cause, said Jennifer Jones of the National Interagency Fire Center in Boise, Idaho.
On land managed by the U.S. Forest Service only, the center found 17 such wildfires in 2010, 28 last year and 13 so far this year.
This year, the Bureau of Land Management said 11 of 31 wildfires it has battled in Idaho have been sparked by shooting activities.
In New Mexico, state forestry officials said a landowner was target shooting when one of his bullets hit a rock and sparked a small blaze. "This is a sign that we are very dry," said state forestry spokesman Dan Ware. "We're starting to see very unique ways of fire starting."
Officials at Arizona's Tonto National Forest had seven wildfires caused by firearms in 2010, 10 in 2011 and at least five so far this year. The potential for fire is so great that shooting for several years has been prohibited on BLM property in the Phoenix area.
In one case in the state, prosecutors said five friends at a campout and bachelor party set off an 18,000-acre fire May 12 when one of them loaded an incendiary shell, which burns rapidly and causes fires, into a shotgun and pulled the trigger.
Meanwhile, firefighters are wary of more wildfires with the arrival of the Fourth of July holiday.
"The Fourth and the 24th — our Pioneer Days — are all popular times to go shooting," Aposhian said. "Many people use these times to show patriotism as well as support for the Second Amendment."
Brian Skoloff reported from Salt Lake City. Associated Press writers Felicia Fonseca in Flagstaff, Ariz., and Susan Montoya Bryan in Albuquerque, N.M., contributed to this report.