I see there is a company that makes a switch for a glock to turn it into full automatic. What would I need to do to get a class III permit to own one of these? If this is doable what would the permit cost? I have had my FFL license for about 3 years now.
An individual can only take possession, using the proper forms and procedures (Form 4 or 5), of machineguns that were registered prior to the cutoff in '86. These are termed "Transferable Machineguns". It doesn't matter if you have an FFL or not, provided you do not have an SOT (more on that later).
These F/A glock "switches" are most likely illegal. The only way they could be legal is if they are considered by the ATF to be a registered auto-sear and were registered prior to the cutoff in '86, which is very unlikely.
If you have an SOT of the right class (2 and 3 are most common) associated with your FFL, you may possess properly-transferred post-86 machineguns for demo purposes to L.E. To get these you must have an appropriate "demo letter" from the department or government entity.
PS- I apologize for the delay. I didn't realize I was the moderator here!