The NFA can be confusing, but one of things not regulated in creating a rifle out of a pistol. There are several pistols worth looking into to turn in rifles. There are AR-15 pistols, AK-47 pistols, Glocks, and many others including new ones coming on the market even today.
What can be confusing is what is the difference between a rifle, a short barreled rifle (SBR), or any other weapon (AOW). A rifle is a firearm that came from the manufacturer with a butt stock and at least a 16in barrel. An SBR is the same, but has a barrel under 16in and is controlled by the BATFE which requires a tax stamp. An AOW is also controlled by the BATFE and requires a tax stamp and is a catch all category to include things like a pistol that uses a forward grip, pen guns, cane guns, etc.
We will be focusing on the pistol to rifle conversion today and I will be using a Draco AK-47 pistol as an example because I am currently working on this as a project. Converting a Draco pistol to an SBR is as easy as apply for a tax stamp and then slapping a butt stock on the end once it is approved. From there you can change it up pretty much however you want.
When turning a pistol into a rifle you have many more options to attain the 16in barrel. The easiest thing to do is get a muzzle device that is the length needed to measure 16 inches from the bolt face to the end of the device when mounted. This can be accomplished by several different means. Short barrel extensions can be purchased to lengthen the barrel for your muzzle device desired, or even extended muzzle devices can sometimes be purchased. You can also purchase a fake, or real, sound suppressor and use that. The key to useing any of these devices is that it is “permanently attached” This is where it becomes a little bit of a gray area. Most people get away with a tack weld, and some weld the whole device on. In my, non- legal opinion, I would use the tack weld.
When dealing with NFA type things it is good to ask around with credible people about info to help you out as being caught with an illegal firearm can be rough on your pocket book and can land you in prison for a long time. Don’t be afraid of it though. Just be sure to know the laws!