[Mike of the Mountain]

Originally Posted by Craig Larter

One think I have learned is the material used to take up stack height makes a difference in pressure. In one load I used four 1/8" 10ga nitro cards as filler, in another, the same except I used a 1/2" fiber wad. The nitro card load averaged 8200PSI, the fiber wad load average 6833psi. Velocities were similar at 1130fps. It must be that the fiber wad is softer and compresses on ignition.

Yes, fiber wads result in lower pressure. That’s why when pressures are too low we use the hard fiber wads.