> hard to mess up

I think it depends a bit on technique and choice of firearm. Some people foolishly put a gun in their mouth and assume it will definitely kill. But it's entirely possible to miss the brainstem and just blow off the side of your face instead. Now you are alive but mangled.

Something like a shotgun is probably a bit harder to screw up.

But personally I'm far too chickenshit to use a firearm. I'd probably try to find someone who'd sell me fentanyl, were I interested in terminating my own existence. At the moment, however, I'm far more likely to suffer an existential crisis and so I've zero desire to answer life's greatest question any sooner than strictly necessary.