You just completely switch the argument with a red herring.
It doesn't matter whether that person is a safe gun owner or not here. And a lost round of ammunition is such an armchair take it makes me question if you should even have an opinion on the subject...
A round of ammunition in your bag should not equate to years of prison, end of story.
I had a box of .22 rounds in my backpack that I was bringing back from the gun store. Lo and behold it was loose, and some had unknowingly fell into my bag. I didn't notice they were there for years until I did a deep clean of my backpack. No one counts throw-away ammunition.