A Primer Type Change CAN Alter Velocity and Pressure

July 9, 2022 The answer is yes. It is important to remember that changing primer types can affect your load’s performance by affecting velocity average, velocity variance, accuracy, pressure, and pressure. There are many variables that can affect the performance of primer types. It is impossible to predict which primer type will be better or worse. It will depend on your cartridge, powder, barrel, and even the mechanics in your firing pin system. Glen Zediker recommended decreasing your load ONE FULL GRAIN when changing to a different primer type, one that you haven’t used before.Interestingly, however, a shooter on another forum did a test with his .308 Win semi-auto. He used Hodgdon Varget powder, Sierra 155gr Palma MatchKing (item 2106) bullets and found that Wolf Large Rifle primers had slightly higher velocities then CCI-BR2s. The speed difference between the middle and lower values of the charge weights varied, but it was interesting that the Wolfs provided more speed. The shooter noted that the Wolf primers were clearly hotter and had an almost equal or better ES average. See the table:Varget.308 load 45.5 grain 46.0 grain 46.5 grains CCI-BR2 Primers 2751 Fps 2761 Fps 2783 Fps 4798 fps Wolf LLR Primers 2757 Fps 2680 fps2798 fps Speed 6 fps 19fps 15fps You cannot extrapolate too much to the table. This table only includes one gun, one bullet, and one powder. As they say, Your Mileage May Vary (YMMV). This illustration shows that substituting one component can result in significant changes. It is possible to repeat the procedure in multiple chrono runs. A 19 fps increase (with the 46.0 gr powder load) can be meaningful. An additional 20 fps may result in a better grouping or accuracy node. (Bite: Speed is not always better for accuracy. You have to test it to find out. WARNING: You should be cautious when switching primers. While speed is attractive, you should also consider that the primer with higher pressure may produce more pressure. When changing any component of a load, it is important to monitor pressure signs. Glen Zediker suggests that you reduce your load by ONE GRAIN when switching to a different primer type.
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