I've not done it but, was a witness....
To some extreme damage. The names are changed to protect the guilty.
In a city in SoCal, to remain nameless, at an indoor range that had three, fifty foot long by eight bays wide, shooting ranges, I watched this happen.
The last shooting bay could be used for rifles when the business was slow. The calibers were: 22 LR, 9mm, 40 S&W and 45 ACP, all clearly posted on the far wall of that particular shooting bay.
Well, "Eddie" was the young college student who was at the counter at the time. I had gone in and was shooting in range 2, bay 8, just close enough to see the guy with the rifle take a bench rest solid position and fire. Ka BOOOOOM!!!! Followed by another and another and another. This was NOT any of the calibers posted on the wall.
I went to Eddie and asked what was going on. He said it was OK. I knew better and called the owner "Vince" and told him to get down here soon as there was a guy putting holes in the back stop!
Vince did get there in record time and sure enough there were 17 holes in the 1/2 steel plate and LARGE pock marks in the concrete wall in back of that.
When Vince found out the caliber he raced to Eddie and asked why he let the guy shoot on the rifle range. Eddie said, "well, you told me that if the rifle caliber was smaller that 9mm they could shoot. Isn't 7mm smaller than 9mm?"
Needless to say, that was Eddie's last night at the counter and Vince had to fork out over $3k to have the back stop rebuilt.