Maybe. I haven’t done the math.
One of ways the ATF defines a firearm is "any weapon that can be converted to expel a projectile using an explosive."
If you don't WANT it to be considered a firearm maybe it's sufficiently corroded such that it's no longer true that it could expel a projectile using an explosive, and therefore is no longer a firearm. In that case, if you hit someone with it, it goes back to being an armament, but no longer a firearm.
That is of course unless you melt the metal down and turn it into some kind of lower receiver. It would go back to being considered a firearm by the ATF.
Whether or not it's a firearm depends on your context. If you and all your friends disagree it's a firearm, in that context it is not. In other contexts it is.
Words are really just illusions though. It's equally true that there are no firearms, because firearms are just words. It also is true that any and all matter is a few steps away from being a firearm. Where do you end and I begin? If we get quantum mechanics into it, maybe everything already is a firearm.
If you have a reason why it's bad then just say the reason. Don't ask insinuative questions.