Is somewhere written rules for flashbang grenade? Could not find it yesterday, so I went with modified flash-pack.

I hope they've been toned down a bit. IIRC, in 3rd edition, they dealt stun damage twice, once from flash, once from sound. Of course, niether could be resisted by armor either, so it was usually a pretty vicious combo.

Flash-Bangs are described on page 313 and the table with their stats is on page 314. They do 6S damage distributed evenly over their radius.

In prior editions of the game you had to sort of home make a flash-bang by using the Dual Charge grenade rules and combining a Flash grenade with a Concussion grenade. Flash grenades weren't resisted by armor, and only inflicted temporary vision penalties. Concussion grenades were resisted by impact armor, but were reasonably weak due to a base damage of Moderate. Their description of how a flash bang works appears off to me, btw, like they're mixing up how real stun grenades work with thermobaric weaponry.