If you quarry requires #4s, Polywad's 60X is a unique choice. I think the pressure is a bit more than 8k psi(8k psi<pressure<9k psi). I shoot quite a few of those and you can't stand too many in short sleeves. I've let a friend, with an A5 configured with the max number of friction rings, bum a few when he was low and the A5 wouldn't cycle.

Kind Regards,

Raimey
rse