It is not a case of legality within a State but the legality on the Federal level and the Federal law trumps Sate law. Readers of this thread need to understand this and know they need to be in compliance with Federal law also, not just State law.
Bch – I'm hardheaded on this subject because the fines are so great, $250,000/10 years. In reading about your encounter with a short barreled shot gun in your back seat. I have no reason to doubt you nor am I doing so. BUT, you were extremely lucky that the officer didn't know/care the full law or you may not be here conversing on the subject. I don't believe I stated that this gun is specifically illegal in Wyoming, just that you needed to heed Federal law also (If you are in violation of Federal law then the gun is illegal no matter where you are (further, suppose you were in New Jersey with this rifle or your shot gun you would be facing State and Federal charges)). In your case, had the State officer requested to see the tax stamp for your weapon you would have been in trouble and yes a Federal agent would have made the arrest.
I find it of no surprise that an officer doesn't know all the firearms laws, this happens often. I've had local police ask me questions about firearms including certain legalities. In Ct we still have an “Assault Weapons Ban” that preceded the Federal ban that has expired, many officers are confused about specifics of the law. Across the street from me is an FBI agent that I have talked at length with. Without going into specifics he has told me of wrongful arrests he has personally seen made on weapons charges because so many agents don't know all the laws.
Following are a couple sites with information on how to legally purchase a rifle such as the one in this thread. For the record, the rifle in this thread could never be legal as is due to the fact that it was made in the current configuration without following proper procedure.
http://www.class3weapons.com/class_3_faq_class_3_weapons.html
Please visit the above site and scroll down to “Process for Obtaining a Class 3, Title 2 or NFA Weapon”
You will read that you must carry the tax stamp with the NFA item at all times in case the legality of the item is questioned by law enforcement.
http://www.guntrustlawyer.com/states/wyoming/ - This site supports the claim that a rifle such as the one in this thread is legal in Wyoming (but you still must be in compliance with Federal regulations).
Wyoming (WY) What NFA Firearms can I own?
There are several type of Class 3 items that are restricted by the National Firearms Act.
Each state can impose additional restrictions on the sale, purchase, and transfer of class 3 firearms in addition to the compliance that is required with the national Firearms Act.
In Wyoming you can own the following items that are regulated the the National Firearms Act
Machine Guns
Silencers
Any Other Weapon (AOW)
Destructive Devices (DD)
Short Barreled Shotguns (SBS)
Short Barreled Rifles (SBR)
In Wyoming you cannot own the following NFA restricted items.
None