One of the most common questions or misconceptions is regarding the ability to make a Machine Gun by using a Gun Trust. While you can make a Machine Gun with a Gun Trust, the process or the cost is not what most would consider acceptable. First you are not making a machine gun as you might expect using an ATF Form 1 but you must first start with a legally transferable pre 1986 full auto sear. This is in the 10-15K range and is by itself a Machine Gun. Now that you have a legal machine gun, you can modify almost anything and essentially create a new Machine Gun.
If you purchased a Pre 86 sear, you could change out the pins, add a left hand magazine release, change the trigger, and even build it into 300 blackout if you wanted. Once you were done, you would essentially have a new machine gun but it would be 10-15K more than what the police or military could purchase a current model.
So while you cannot technically "Make A Machine Gun" you can modify a legal transferable machine gun.