|Myths and Basics of black powder shotgun|
By Michael King
I am probably a better gunsmith than marksman so this issue I wanted to share a little of what I have learnt about blackpowder shotgun.
Firstly I have discovered that coarser powder is definitely better for shotguns. It seems to me that the slower ignition and lower peak pressures of the coarse powders give more even and consistent shot patterns.
Secondly, it appears that the amount of powder is directly proportional to the amount of shot used in order to maintain a good shot pattern. The general advice seems to be that more powder is best and my experiments clearly show that this is not necessarily incorrect. Too much powder really blows the shot pattern. So much so that at 25m the gaps between the pellets are great enough for you to completely miss the bird with a perfect aim. The best shot patterns from my experiments result from using roughly the same volume of powder as shot. Using more powder than shot opens up the pattern dramatically and using less powder shot that shot closes the pattern. You can play with the ratio safely within about 15% of the equal powder/shot ratio only before the pattern really becomes scattered and inconsistent. Experimenting with the ratio within that 30% tolerance is like changing chokes on a modern shotgun.
The lubricated cushioning wad seems to have almost little effect on the shot pattern however of course using a lubricated wad drastically reduces fouling with obvious benefits. Lubing the wads with a 50-50 mixture of beeswax and copha seems to work well enough.
It is vital to not ram the cardboard disc over the shot too hard. If you do this seems to deform the shot and impact it in the barrel so that it emerges from the muzzle in clumps leaving a very irregular shot pattern with large gaps in it. So be very careful when you seat the last cardboard disc over the shot.
You also need to acquire the bird at least 10m sooner than with a modern shotgun for two reasons. One is that the muzzle velocity is about 200 feet per second slower than a cartridge gun and the other is that with no choke the dispersion rate is much faster.
Having shared this information it is only my observations from some experiments I have conducted. Each gun needs to be worked up but these seem to be appropriate rules of thumb for optimising your loads.
Happy shotgunning! I hope this helps you to powder those birds.