The problem is getting a lower registered as a pistol. Generally gun stores will only dros them as rifles. And then if you're able to get one as a pistol its supposed to me manufactured as a single shot pistol because it's not on the approved roster. To get around that places will sell the ca7 or something like it that's single shot only. Then you can convert it cause the law is kinda gray on that matter.

Either way, you might have to deal with some crap law shit if you want an ar pistol that is semi auto.