Primer Wads

[Bullshot]

jgh,
I have come to the conclusion that damping the flame causes a much slower form of ignition.
this in turn tends to make black powder ignite in a way that resembles the progressive burning of smokeless.
you will notice the improvement more as ranges increase, possibly due to improved velocity standard deviation.
ultimately who cares why? if it works, do it.
keep safe,
bruce.

This may be right as we have shooters in our club who say one needs the magnum primers and others who say no.
My best guess is as follows: The powder is covered with graphite which accounts for the dust we see over recently poured powder. Some of this dust enters the primer hole and forms a bridge, which makes ignition erratic, therefor erratic results downrange. Mag primers reliably break up this bridge and cause uniform ignition.
Over Primer Wads (OPW) stop the carbon bridge and therefor its maleficent effects.

Good shooting.