You will also have to get a release through the D.A. GOOD LUCK WITH THAT. Then they will do Ballistic testing on it and record the results for future use. IF you ever get it back Don't ever do anything Dirty with it because they will know where the bullet came from.
Also check with them about the size of the gas port on the barrel. Have had issues with other manufacturers and it wound up being the gas port was under/over sized. Most barrels are mass produced and errors are made with the port diameters.
Definately go through the process to get your UPIN. I went through it many years ago because of getting delays all the time. It takes a while for processing but they will give you a UPIN or will tell you in detail what the issue is. I got involved with an FFL who I used often when I put a...