I was out shooting the other day and saw someone shooting with an oil filter and went over to ask em about it. It turned out it was a real one, registered and all (stamp). He was using it on a 300 blackout with 247 grain subs, it wasn't as quiet as a commercial can but it sure didn't sound like a gunshot. standing right next to him I didn't need ear pro, and it sounded like you dropped a large book on the floor, more of a woomp than a bang. He shot one without the can on it and it was not terribly loud but it sounded like a gunshot. JIC anyone had ever wondered if they were effective on something larger than .22.