really the forms are not that complicated, and are self explinatory. But for those that have questions what goes in the blocks, this should help.
4a, you put the name and the location of the original manufaturer of the firearm, which is the receiver. This can be found right on the receiver itself, ie VECTOR ARMS, INC, NORTH SALT LAKE CITY UTAH.
4B: you put SBR there
4C, caliber goes there, it will be stamped on the receiver, ie 9x19mm, .223, 40 SW, etc..
4D, model:that will be stamped on the receiver, ie V53, CA89, etc..
length of barrel, and overall lengeth: you can measure those yourself, each will be different depending on the model. for OAL that is with the stock extended.
4G serial number: it's on the receiver
4h, that is if you want to engrave other markings on the thing, ie, your name
4i, I put collecting, target shooting, and all lawful purpose. you can use that, or put something else.