I have seen a few scopes go tits up, but not many. I have seen several fog up but that can sometimes be chalked up to user error and may or may not be an actual failure.
Ammo failure? I don’t think I have ever seen an issue there that couldn’t be traced back to user error—-normally either a step missing in the reloading process or using a new lot of a component and not test firing the new combo out.
Rifle malfunction? I have seen quite a few. Triggers suddenly not catching on the sear despite never being messed with and extractors breaking. I have seen several trigger/actions freeze up despite being degreased and dry graphite lubed. I have seen a few stocks break in half. They can again mostly be attributed to user error, especially the cleaning and lubing of them for the conditions as well as being rolled over by horses/four wheelers.
Equipment breaking due to normal use is rare IME, other than the really cheaply made junk of course. The non messed with trigger issues are about the only exception.
