Check out this Airsoftjunkiez Custom VR16 Saber CQB M-Lok HPA. Just like their other custom HPA airsoft rifle projects, this allows you to choose your HPA engine and this will be configured at 320 - 390fps on 0.20g BBs as well as the rate of fire will be around 22-33 BBs per second. Just customise it further by going to the product page and select the rig you want for it.