20 or 24" depending on what is easier to get for which model gun. There was hot demand for 20" barrels but it has mostly died out. First because they mostly ship with 24" ones in the popular brands and second is that in most locations, the "right" setup is with a 12 round tube. At that point the tube is longer than a 24" barrel, so why spend money trying to get a 20" barrel for something shipping with a 24. If you can get one with factory fixed sights at that length, that's really the sweet spot.
The shotgun in 3 gun is stupid and entirely impractical. it's an ungainly mess that you would never try to manipulate in an interior space outside of a warehouse or a big box store. IMO it should be 18" barrels with 8 round tubes as the norm as that is a very handy package when set up right. But that's not the way things have shaken out. It's the gamiest part of the game.
That being said, 18" barrels that accept chokes can be at a disadvantage at some matches. 18" cylinder bore barrels with no choke are near useless for 3 gun. I tried 18" with a choke because NJ (and 18" with a 6 round tube is not a bad setup in terms of looks or ergonomics), but outside of it being a mossberg 930 and having the associated reliability issues and problematic manual of arms, it just was sub optimal with choke selection. Where others shooitng 20-24 could put on a cylinder choke and shoot whole arrays while picking up freebies from the spread, I'd start getting donut holes in my patterns with some ammo.
Shotgun isn't about what is practical or most right, it's about what is the least wrong choice for a competitive advantage. Given that, it's a place where the wisdom of the crowd is a bit more correct than typical.
Work around - don't get the real id. Do it online. Then pick a different less busy line in the form of getting a passport card. It is accepted for flights. Heck a passport might be as well if you already have one.
Thanks - I was fairly sure that was the case. If anyone else is interested: I found the guidance form the NSSF here ( http://www2.nssf.org/l/127421/2020-04-28/42prlx ) that says as much and even references/links the ATF guidance for these situations.
You are going to be fine. oakridge is saying exactly what you were told by your local PD. While your physical DL shows it expired, the computer systems will show it was extended due to the wuhu flu and, therefore, valid.