Doubletap Ammunition Tactical 300 Blackout 240 Gr Sierra MatchKing. It is also an excellent defensive load with excellent penetration and expansion. Specifications for Doubletap Ammunition 300BK240MK Tactical 300 Blackout 240 Gr Sierra MatchKing H: Manufacturer: Doubletap Ammunition Caliber: .300 AAC Blackout Number of Rounds: 20 Bullet Type: Boat Tail Hollow Point (BTHP) Bullet Weight: 240 grain Cartridge Case Material: Brass Muzzle Velocity: 1025 ft/s Application: Competition Primer Style: Centerfire What is Doubletap Ammunition 300BK240MK Tactical 300 Blackout 240 Gr Sierra MatchKing H good for? The manufacturer thinks that it is best for competition.