The difference in shotgun primers arises from the chemical composition of the primer compound that is found within the primer cap. Depending on the composition of this primer compound, the velocity of the shotgun shell can significantly increase or decrease.
A study conducted by Tom Armbrust on how different primer compositions affect the overall velocity of shotgun shells found that there is a pressure variation between shotgun shells made by Federal, CCI, Winchester, Remington and Cheddite of nearly 2,640 pounds per square inch. This change in pressure changed the velocity of the shotgun ammunition by nearly 34 feet per second, with Federal primers causing the highest velocity, followed by CCI, Winchester, Remington and finally Cheddite. This suggests that the chemical composition of primers created by different manufacturers increases or decreases the velocity of the shotgun ammunition being fired.
Although the composition of the shotgun primer can vary depending on the manufacturer, all shotgun shell primers are labeled as No. 209. A shotgun shell primer is also significantly larger than handgun and rifle primers, which account for the larger base of the shotgun shell. Additionally, the base is also shaped differently than rifle and handgun primers due to the "battery-cup" design of the shotgun shell primer.