If you’re making a semi-auto, it must be a closed bolt design, and the sear must be designed to not reset until the trigger travels forward. It’s much easier to make an open-bolt SMG than a semi-auto pistol.
Also out here in the Wild, Wild West (aka Arizona) one can make pretty much any firearm they wish as long as it isn't full-auto or has (IIRC) a barrel over a 1/2" thanks to the last governor.
Anyhoo, the point is it varies on the gun laws depending on where you live.
> Also out here in the Wild, Wild West (aka Arizona) one can make pretty much any firearm they wish as long as it isn't full-auto or has (IIRC) a barrel over a 1/2" thanks to the last governor.
Federal laws still apply, and the NFA in particular is what makes DIY firearms complicated. I'm in Arkansas, and it's about the same here as Arizona.
Funny. I live in FL where a carry permit is relatively easy to obtain. (Interesting that many local MDs in SW FL have one) But the Mossberg Shockwave loophole is hilarious. Take for example New Jersey's supposedly highly restrictive gun laws. An assault weapon includes A semi-automatic shotgun with either a magazine capacity exceeding six rounds, a folding stock or a pistol grip in their NJ Administrative Code Title 13. Yet a Mossberg 590 Shockwave 12ga 14 inch 6-shot with a handle grip resembling an old flintlock pistol is legal.
The handgun portion didn't survive, but the minimal length requirements did.
Also, interestingly, it wasn't a ban but a tax. Congress at the time believed they didn't have the Constitutional authority to ban any class of firearms, so they instituted a prohibitive tax ($200) on short-barreled rifles and shotguns, "destructive devices", and automatics. There's a $5 tax on "any other weapons", which these days mostly applies to guns that don't look like guns.
Bear in mind that $200 in 1934 is about $3,700 today. At the time, you could mail order a .45 Thompson submachine gun for about $200, so the law effectively doubled the price. They were advertised as self-defense weapons for property owners: https://gastatic.com/digest/wp-content/uploads/2016/04/tumbl...
Automatics weren't banned until 1986, and even then, they weren't technically banned - they just require that $200 tax, and it's not possible to pay the tax for one made after May of 1986.
You can also have an open bolt semi there are quite a few conversions that didn’t went closed bolt.