I might just be confused because it doesn't specifically single out each item is ok with a tax stamp.
Other states specifically single out each individual item that is ok with a tax stamp. I got what is below from nra ila.
Machine Guns, Magazines , Ammunition, etc.A machine gun is defined as a firearm designed to discharge more than one shot by a single function of the trigger. Mont. Code Ann. 45-8-302(2).
It is a felony to possess (or use) a machine gun in the perpetration or attempted perpetration of a crime of violence (any forcible felony, robbery, burglary, and criminal trespass) or for any other offensive or aggressive purpose. Mont. Code Ann. 45-8-303, 304, 302 (definitions). An offensive or aggressive purpose is presumed when the machine gun is in the possession or use of any person who has been convicted of a crime of violence. Mont. Code Ann. 45-8-305.
This law does not prohibit or interfere with the possession of a machine gun for scientific purposes, or the possession of a machine gun that is not usable as a weapon and possessed as a curiosity, ornament or keepsake, or the possession of a machine gun for a purpose manifestly not aggressive or offensive. Mont. Code Ann. 45-8-307.
It is a felony for a person to possess, manufacture, transport, buy, or sell a silencer with the purpose of using it to commit an offense, or knowing that another person has such a purpose. Mont. Code Ann. 45-8-336.
Montana has no laws prohibiting or regulating "large capacity" magazines.
Montana defines "armor-piercing ammunition" as ammunition "which, if fired from a handgun under the test procedure of the national institute of law enforcement and criminal justice standard for the ballistics resistance of police body armor promulgated December 1978, is capable of penetrating bullet-resistant apparel or body armor meeting the requirements of Type IIA of Standard NILECJ-STD-0101.01 as formulated by the United States department of justice and published in December 1978." State law does not prohibit or regulate such ammunition, although pursuant to Mont. Code Ann. 46-18-224, anyone who is convicted of a crime in which bodily injury occurred or was attempted or threatened and who knowingly used or carried a handgun loaded with armor-piercing ammunition during the commission of the offense is generally liable to an additional sentence for the offense.
It is a crime to knowingly possess a sawed-off firearm, being a rifle or shotgun that, when originally manufactured, had a barrel length of 16 inches or more and an overall length of 26 inches or more in the case of a rifle, or 18 inches or more and an overall length of 26 inches or more in the case of a shotgun, and where the firearm has been since modified so that the barrel length, overall length, or both, are less than these specifications. This does not apply to firearms possessed by a person who has a valid federal tax stamp for the firearm issued by the federal bureau of alcohol, tobacco, firearms and explosives, law enforcement, a person in actual service as a member of the national guard, a bona fide collector of firearms if the firearm is a muzzleloading, sawed-off firearm manufactured before 1900, or firearms that are incapable of being fired and possessed for educational or scientific purposes. Mont. Code Ann. 45-8-340.
Montana has no law prohibiting or regulating "assault weapons."