Remington Premier 165gr. Core Lokt PSP .300 Short Action Ultra Mag Ammunition 20 Round Box. Remington Core-Lokt Centerfire Rifle Ammunition is precision manufactured, field proven and time tested for unsurpassed performance and reliability. Remington Core-Lokt Ammunition is loaded with legendary Core-Lokt bullets which have dropped more big game than any other hunting bullet. Core-Lokt Bullets are designed with a Jacket and Core that are mechanically "Lokt" together providing just the right combination of expansion, penetration, and weight retention for deadly hunting performance.