The Second Amendment says clearly the Right of the People to Bear and Keep Arms Shall Not Be Infringed. It does not limit the type of weapon to the whims of politicians, because the Founders knew Politicians cannot always be trusted..
The Fifth Amendment says that the government deprive you of property, without due process of law; nor shall private property be taken for public use, without just compensation.
Any legislator supporting the law should be charged with attepting to deprive the citizens of Missouri of their civil right and attempted grand larceny as well as any other criminal charges might be deemed appropriate.