Just my $.02.
First, it’s my belief 99.99% of all shooters are going to be self-policing. At a club event level, I don’t see the need. If there is a value to the event, I can see where some rule conformity might be necessary. But if you are going to check conformity, announce as much in advance as possible. You want to give everyone a chance to check their own equipment.
If your goal is to help shooters know if they are legal before the match starts, chrony before. If your goal is to keep everyone under 20fpe for the duration of the match, then test after the match as well as before the match. That being said, it opens it up to the shooter blaming the gun. And it seems more practical if you are going to do it before, you should do it after too. This will be a hot button topic. however, if someone wants to take advantage of the rules, they will also find a way to skirt the tests.
Give them all the time they need but start the match on time. If they miss a couple of lanes, they will have it fixed next match.
Checking pellet weight and fill pressure I don’t see a need and it would only slow down check in more.
Shots given to check sub 20fpe. 1 off chrony to set reg/spring/gas ram. 2-3 for average.
My experience being checked with the 2% rule was for FPS.
The irony of this is, most rigs are very capable of exceeding 20fpe. However, those same rigs are considerably more accurate somewhere south of 20. As an example, my FT rig max is 22fpe. It’s most accurate at 17.8fpe. A flatter trajectory to or past the faceplate isn’t going to help me if I can’t hit the KZ.