American here, just offering a little clarity. 1st is a very mundane bit of semantics but AR pattern rifles are not typically gas piston but direct gas impingement 2nd bit you touch on is US law on various parts seemingly focused on machine guns. Federal law doesnt outright make posession of auto-sears selectors and such illegal. It gets a bit murky but the key take away is if it can readily convert or allow full auto you're liable to make the government nervous. We get parts kits all the time with complete select fire trigger sets. We dont get in trouble for this unless we modify or situate ourselves in a way that allows us to use these parts for automatic function ie. If I've an AR lower, m16 trigger set, the necessary drill bit and a jig or pattern to mark that 3rd hole its constructive intent. (Of course if you've drilled the requisite hole for the auto sear and dont have a government permission slip, it's an automatic game over) the trigger parts in america is ultimately a misnomer spurred by an abundance of caution (easier to avoid the potential issue altogether as there are several nuances to the matter which ive likely oversimplified) for those who build their own firearms (still legal in most of the country) its their responsibility to ensure what they build isnt capable of firing or being readily modified to fire full auto
@spinner4life2 thanks for the clarification, maybe I misspoke about gas piston while meaning DI (although technically speaking ARs aren't true DI either but more internal gas piston ) thanks for clarifying on the selector parts , I was miss informed that you couldn't own such parts without the required hoops being jumped through
@HTISAirsoft fairly common misconception. Part the government is most concerned with is if a firearm can be readily modified to accept the parts and if the parts will constitute a giggle switch. Have built a number of firearms from parts kits wherein the donor weapon was a de-milled machine gun, LOTS of the components in question have passed through my hands, law enforcement doesn't even flinch when I mention "it was a parts kit build" and explain what all that entails ie. "I had to do the semi conversion on the trigger pack myself as nobody else in the area was familiar with this platform"
