Something similar ocurred at the range a couple of weeks ago.
A guy down the line from me walked over. He hands me a ctg. and says"What does this say?"
I had no idea where he was going with this. Gist of story: He was shooting a .260, and had a 7mm-08 round mixed in. He only noticed it because the bolt didn't close normally.
Here's the scary part... This guy doesn't reload. He had two or three different rifles, but they were VERY different, as in .243 WSSM, .260, and '06!
This 7-08 cartridge came from a (large outdoor) store mixed in a box of .260s. Prolly the result of someone's cartridge comparison discussion. At least I HOPE the incident was an accident!!!
I did call & notify the store, so they could check the stock on hand. I'm sure someone somewhere had an unexplained flyer from a 7-08!
Just goes to show, you can NEVER let your guard down... Ever!