Very cool novelty! - FRT Triggers FRT-15L2 AR-15 Forced Reset Trigger, 2 Position, Drop-In Compatible w/Anti-Walk Pins

This trigger is firstly a novelty, but it is very fun. If you just want some fast fun at a lower cost per bullet, you can definitely tune an AR9 and mag dump some 9mm. Be sure to call your preferred gun range first to make sure you're allowed to shoot with this trigger first. Many indoor ranges aren't a fan of the high rate of fire because they don't want customers shooting the ceiling. My preferred range wants you to do a qualification course to show you know how to handle the firearm before they'll let you shoot.