Firearms are a subject that many people not familiar with firearms say have few regulations. The regulations for firearms are located in Title 27 of the Code of Federal Regulations. So lets go through a few of those.
First off, what is a firearm? The regulations define 4 things which are firearms and 1 which is not. 1) any weapon which will expel a projectile by explosive force. 2) the frame or receiver of #1. 3) a muffler or silencer. 4) a destructive device. And the item which is not is 1) antique firearm - any firearm manufactured in or before 1898 or replica of such firearm not designed to take centerfire or rimfire ammunition.
So what are the ramifications of this. Well, lets use the Mosin-Nagant as an example. This rifle has been manufactured since 1891. So by the definitions above, those made from 1891 to 1898 are not firearms. Those made since 1899 are firearms. Even though they all fire the exact same ammunition and in most cases their parts are interchangeable. So the same gun is a firearm but also not a firearm. The implication of this ridiculous designation is that a Mosin-Nagant built before 1898 is not subject to the sale and possession restrictions of the regulations. So, prohibited persons (criminals, mentally ill, etc.) could buy a pre-1898 Mosin-Nagant and not break any law. Also, anyone could have a pre-1898 Mosin-Nagant shipped to their door - no background check, no waiting period, no nothing. But if it was made in 1899 all of the rules apply.
Next, a frame or a receiver is also a firearm. When transporting firearms on aircraft they have to be declared and in a locked case. And the case cannot be opened (even by the TSA) except in the presence of the owner. A frame or a receiver is a single part. It is the part that all of the other parts attach to. By itself, a frame or receiver is incapable of firing a projectile (no firing pin, no barrel, etc.). The BATFE has further ruled that a receiver/frame has to be more than 80% complete to be a receiver/frame (and therefore a firearm). An AK-47 80% receiver can look like a flat sheet of metal with some holes in it. So, I can put 100 of these in my checked baggage and not declare them. Furthermore, I can buy 100 of them and have them shipped to my house (so could a prohibited person) since they are not a firearm, just sheet metal with holes in it. But, if I make just one bend in the flat piece of sheet metal, it is now a firearm and when I go to the airport, I have to have it in a locked case and declare it. If the TSA opens up my bag with flat sheet metal, they are within their rights to do that. If however, they open up my bag with declared bent metal without me present, they have broken the law. Likewise, the same receiver can come pre-bent, just without the holes. Once I drill the first hole it is a firearm.
Next, a sound suppressor or muffler (popularly called a silencer) is also a firearm. So, if I am transporting the silencer on an airplane, I also have to declare it as a firearm (even though I may not have a firearm that it connects to) and have it in a separate locked case (that the TSA can't open outside of my presence).
I have been using the example of transporting firearms on airplanes. Except that falls under the TSA jurisdiction and they are under 49 CFR Subtitle B Chapter XII. Unfortunately, they don't define the term "firearm" so, that 1891 Mosin-Nagant (which according to the BATFE is not a firearm) may have to be declared as a firearm at the airport; and that sound suppressor (which according to the BATFE is a firearm) may not have to be declared. It's a little hazy as to what is what in the world of federal regulations, especially when you have to jump from one agency to another.
Let's look at another area. Importation and manufacture. Here are three rifles. One of them is illegal.
If you guessed the middle one, then you would be wrong. That one is perfectly legal. The top one is the original configuration (minus the magazine) with all Russian parts. And, I lied. The bottom is also the exact same as the top one. However, if I put the American made 30-round magazine shown in the middle on to the other configuration, it would be illegal. If I switched out the 30-round magazine in the middle with the factory provided 10 round magazine, the middle one would be illegal. Regulations require imported rifles to remain in their imported condition, or have a minimum number of US parts installed. Any less than the minimum parts and you have an illegal configuration (which I believe is a felony).
What is most hilarious about this, is there are several internal components which count and you wouldn't be able to tell without disassembling the rifle - except that many of these parts usually don't have a "made in the USA" stamp. So, the only way to show compliance would be to save your receipt - unlike the tax code, there is no time limit so you would need to save these receipts forever. But if you happen to be a closet machinist and manufactured your own parts (which is perfectly legal), you really have no proof that they are USA made parts (unless you video documented the manufacturing process). Talk about a regulatory burden.
One of the types of Federal Firearms License is a Curio & Relic License, or a collectors license. It allows holders to purchase firearms for their private collection that meet certain criteria (mainly being more than 50 years old). They still shoot modern ammunition and some people even use them as their daily carry guns. The process involves a background check by the FBI. Purchases can be made from other FFLs by mail shipped directly to your home. Firearms not on the C&R list, though, cannot be shipped to your home, they must go through a retail FFL. So, let's say I want to buy two guns from Southern Ohio Gun Company. Both in 9mm Makarov. One is a C&R, the other isn't. For the C&R gun, I give them my FFL license number and they ship the gun directly to me. For the other, I have to find an FFL near my home (in my state) to do the transfer. SOG sends the firearm to the FFL, and then I go to the FFL. Do I show them my FFL? No, since this isn't a C&R gun, that won't work. They have to fill out the 4473 and call in to the NICS to do a background check (even though I just got the other gun in the mail the same day). Unless, I happen to have my concealed carry license, in which case they fill out the paperwork, but don't need to call it in (at least in my state, other states are different). Oh yeah, and I probably had to pay them extra for the gun. So in a nutshell, one gun is 51 years old and is shipped right to my door. Another is 49 years old and I have to pay more and involve another company including filling out paperwork. The guns are functionally identical. Makes perfect sense, if you work in the government.
Finally, let me look at another issue. You can have a firearm registered as a short-barrelled rifle if the barrel length is less than 16 inches. So, hypothetically, let's assume you have two of the same rifle, one with a barrel of 16 inches, and one with a barrel of 15.9 inches which is registered with the BATFE. The short barreled rifle is registered by the serial number which is on the receiver, not the barrel. Both operate the exact same (they are both semi-automatic). One day after shooting, you happen to be cleaning both of them and inadvertently assemble the shorter barrel on the non-registered receiver. You have committed a felony. Even though you still own the exact same weapons as before. But don't worry, you're only going to get caught if you tell someone, so quickly you disassemble them and reassemble them correctly.
People like to think that regulations help us and keep us safe. They couldn't be further from the truth. In many cases the regulations are impotent or unenforceable. In others, they are contradictory across departments. Most of them have little semblance of protection. I have only talked about four examples out of thousands. These four do nothing to keep us safer. Would we be better off without these regulations? Absolutely! But no politician wants to go on record as repealing our gun laws. Even if they are stupid and do nothing to help us. The saddest part about all this, like calling the IRS for tax advice, my analysis above could be wrong. I may have said something was legal when it really wasn't, and vice versa.
So the next time someone says guns aren't regulated, laugh in their face. And don't be ashamed if you spray some spit while doing it.