Winchester Triple Seven Primers For Sale. Winchester Triple Seven Primers are developed particularly for muzzleloading and are less explosive than standard 209 Shotshell Primers. Milder primers do not drive the powder charge forward, which helps maintain constant velocities and reduces the creation of crud rings. The consistency and sensitivity of these primers are thoroughly tested at temperatures and circumstances far beyond the typical range of use. Winchester ensures greater sensitivity for more positive shooting in all firearms, uniformity in size and quality, and stability in high temperatures and humidity. These primers are not intended for use in shotshells; they are solely intended for use in muzzleloading rifles.