Were any restricted guns used in The First Purge?

No weapons higher than class 4 were used.

A very well researched blog post helps to define what the different classes of weapons are. The article cites the National Firearms Act of 1934 for its definitions.

Question: What are Class 1, 2, 3, 4 and so on Weapons and an example of each?

Answer: I will answer this question correctly and as best as I can. The NFA (National Firearms Act enacted on June 26th, 1934) classifies all weapons that are sold, manufactured, imported, exported or owned by Americans, into 4 major Categories. A Weapon is defined as: any instrument or tool that can be fashioned and wielded for the purpose of killing (animal or human) or inflicting bodily harm on others. It is by this definition that the TSA is able to call a box knife (a tool most commonly used for cutting boxes and tape off of packages) a weapon, since it was used one time to hijack an airplane. Now that you have some background on what a weapon is, it's time to define the different classes of weapons as outlined by the NFA.

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Class IV Weapons - The last and highest class of Weapons, sometimes referred to as Class 4, covers what the NFA calls, Destructive Devices or DD's. Destructive Devices are bombs, grenades, nuclear weapons, flame throwers, dynamite, rocket launchers, tanks, Javelin Missile Launcher, Harrier Jets, and so on and so forth. Class 4 Weapons or DD's cover anything that explodes, shoots flames, or launches an exploding device. Class IV weapons are illegal to own, manufacture, sell, trade, import, export, or own parts for, by any American citizen other than properly licensed LEO's, Military, and government officials.

_{Read the full article}

Using this definition, it is safe to say that no weapons higher than class 4 were used in The First Purge or any of the other Purge films. Its seems that the point of this rule is to basically allow any and all types of weapons. I do not know what would be considered higher than class 4 as it is not defined in the National Firearms Act nor is it defined by the film. I would imagine biological and nuclear warfare probably would be classified as above class 4.

Reading this years later and, yes, class IV weapons do include nuclear devices, and it is actually possible to import nuclear weapons and/or weapons grade nuclear material through the ATF.

As for The Purge, I have no idea how a willy nilly civilian could get any nuclear payload but it would be technically legal to detonate it during the event.

My personal favorite would be a fully loaded R-39 Rif, aka SS-N-20 Sturgeon by Americans. It is a Russian three-stage ICBM that has the capacity of ten smaller individual 500 kiloton nuclear warheads, capable of destroying a small city each and irradiating hundreds of miles of estate, depending on the area.

We never see any class 4 weapons used by the regular purgers in the movies, so I think that it was class 4 and up that were banned.