Yes, Thunder's rant about stuff. Not only that, but many guns have quick change springs/cylinders, or NPAS or similar valves for gas guns that allow you to change your muzzle energy on the fly. It's easy enough to chrono a gun with 0.20g or the weight they're using, and then they could alter it up and down themselves. Whatever system you have in place, make sure it's simple to understand and enforce. Spot checks are a good idea, and even a midday chrono isn't bad either. It is each players responsibility to know there gun.

Agreed, BB bastards tend to gain 10fps over other brands

At JOC games they've been using tamper proof stickers to mark PTWs. Sticker goes on the receiver so you can't split it, or sticker goes right on the cylinder, not easily visible, but you can't take it off that cylinder.

More difficult with quick change springs
Polarstars you just zip tie the tournament regulator
GBBRs are much more difficult to keep track of since propane is sensitive to ambient temperature changes.

interesting... that might explain some chrono discrepancies then with game time chrono vs home chrono.