What are the differences between the ATF forms?
When dealing with NFA items, there are different forms that must be used to effect a transfer of an NFA item. I will list the ones commonly used by individuals and when dealing with a Class 3 dealer.
Form 1: A Form 1 is an application to make and register a firearm. If you wanted to, for example, make your AR15 into a Short Barreled Rifle, you would need to file a Form 1. Even though your AR15 is already a complete rifle, you are "making" it into an NFA item, thus the application to "make and register" it. Any time you "make" an existing firearm into an NFA firearm, you would use this form. Form 1's require a $200 tax.
Form 3: A Form 3 is a dealer-to-dealer transfer of an NFA firearm. Lets say I wanted to buy a suppressor from a dealer in another state. I would have to get that dealer to transfer the suppressor to a dealer in my state before I could have it transfered to me. Form 3's usually get processed in a matter of days or a week, not nearly as long as transfers to non-dealer individuals. Form 3's do not require any tax be paid.
Form 4: A Form 4 is an application for tax-paid transfer of a firearm. When you go to buy an NFA item, whether it be from a dealer or an individual in your state, you use a Form 4. If you go to your local dealer and decide you want to buy a suppressor, you must first file a Form 4 in order to have that suppressor transfered from your dealer to you. Form 4's require a $200 tax for all NFA items, except AOW's. If the item being transfered is an AOW, the tax is $5.
Form 5: A Form 5 is an application for tax-exempt transfer of a firearm. Form 5's are most commonly used to will a firearm upon the death of the owner. If your Grandfather passes-on and leaves you his Thompson SMG, you must file a Form 5 before you can take posession of the firearm. Form 5's do not require any tax be paid.