Winchester Triple Seven Primers are specifically designed for Muzzleloading and are milder than typical 209 Shotshell Primers. Milder primers do not force the powder charge forward, helping to maintain consistent velocities and minimize formation of crud rings. These primers are rigorously tested for consistency and sensitivity at temperatures and conditions far beyond the range of normal usage. Winchester guarantees better sensitivity for more positive firing in all guns, consistency in size and quality and stability in extremes of temperatures and humidity. These primers are not designed to be used in shotshells, they are for muzzleloading rifles only.