Before a game, make sure to equip the “Javelin Burst” under equipment. Now, you’ll want to get a shooting frenzy, which will happen when you score a 5x kill streak (in rapid succession). Just wait until you get a large group on enemies and try to kill them all as fast as you can using the grenade apple or tri-stone. When you get a shooting frenzy, your projectiles will begin glowing blue in colour. At this point, switch to the javelin burst and start hitting as fast as you can. If you manage to fire this projectile 10 times within one shooting frenzy you should unlock the achievement.