Legal Question in Criminal Law in California

If you are arrested and charged for that, your legal defense will be that the tube is not the weapon. If you need to hire counsel for your defense, feel free to contact me.

That is not a defense.

Tube type grenade launchers that can fire antipersonnel cartridges, functioning rocket launchers and mortars are Destructive Devices under Federal law, subject to NFA restrictions and felony penalties. California provides felony penalties for possession of any rocket launcher or grenade launcher, whether tube type, cup type or spigot type.