https://streamable.com/lxtv9
Could be faster and you can glitch a triple out of the first grenade with a bit of luck. A lot of the door steps block the explosions so there are places where you should get doubles but don't. The last grenade especially is hard to actually get the double because I think you have to hit the peeking target in the front and only when it's peeking.
Unfortunately there's no category for grenades only so it just comes up in the mixed leader board.