I have in my collection an M1873 "trapdoor" Springfield, an M1896 Krag rifle, an M1903 Mark I, and a 1943-vintage M1 "Garand". That makes for an example of each main standard-issue metallic cartridge firearm used by the U.S. military from the first one in the 1870s all the way through the end of the 1950s.
However, thanks to the National Firearms Act of 1934, I am not allowed to own an example of the rifle formally adopted in 1957, at least not without being fingerprinted and paying a $200 transfer tax, because it is capable of firing more than one round with a single pull of the trigger, which makes it a "machine gun" in the eyes of the law.
Well, no problem, right? Just have the military alter the ones it decommissions so that they are no longer capable of firing in a fully-automatic mode, and then shooters will be able to add these historic Cold War longarms to their collections. Except that the BATFE's current interpretation of the law is "once a machine gun, always a machine gun"; they will not let one of these "machine guns" fall into civilian hands unless its receiver had been destroyed in a very specific manner with an oxy-acetylene cutting torch.
Not everyone is happy about the current state of affairs, of course, and although it's probably so much spitting in the wind, there's a petition.