Last Saturday, April 15, near Grandville, Michigan, residents reported hearing a very loud boom, which spooked a lot of people and led to multiple calls to local police dispatchers. Sheriff’s deputies initially couldn’t find an obvious culprit, though, and the mystery persisted into Monday, when a tipster informed deputies of a possible source: a bachelor party.

By Thursday, according to WOOD, authorities had confirmed the tipster’s claims. The boom, they found, was caused by Binary X, the brand name of a line of so-called “exploding targets”—or targets designed to blow up when shot, so that long-distance shooters know, more or less immediately, if they’ve hit the mark.

The exploding targets are composed of an oxidizer and a fuel. These powders are frequently shipped separately to comply with federal and state laws, because they can go boom when combined (in this case, with the help of a high-velocity bullet impact). Exploding targets are legal in most states, including Michigan, where authorities said that this particular party would not be charged with a crime.

“Detectives with the Sheriff’s Office were able to locate the person responsible for the explosion,” the Kent County Sheriff’s Office said in a press release, and later determined that, “the detonation and transportation of the materials used was done so lawfully.”

If there’s a lesson here, it might be that guns and bachelors and exploding things are dangerous items, so be careful out there.