Pyrodex is bigger by weight than black powder so it take about 1 1/2 tablespoon (or a heaping tablespoon) to equal a tablespoon of black powder. A tablespoon is 1 fluid oz... works out to a little less than 1 oz by weight of black powder.
I'm not a rocket scientist.... but I've shot lots of golf balls in my back yard. The point I was trying to make is you need some pressure or you are going to need more powder to get the same BOOM. If you are shooting lead or concrete projectiles the pressures will be different. I shoot golf balls and blanks.
Lesmore, I think the point that Norm is a trying to make is you need a more consistant method of determing how much powder you are using. A table spoon my hold one fluid oz. but it sure isn't hold hold the mass of one ounce or one ounce avoirdupois. They are two different units of measure. A table spoon is very poor measuring device for measuring powder.
Cannon charges are so large that using standard volumetric tools allow for far to much variation one charge to the next. Cannon charges must be weighed to be consistant.
Trying to substitute Pyrodex for black powder by weight can be done but takes some work. Weigh out the charge weight of the black powder charge your are duplicating. Place that weighed charge in a volumetric measure and adjust the measure to hold that charge. Dump the black powder out and refill the measure with pyrodex. Then pour this powder on the scale and weigh. I would do this several times and take the average of the charges thrown. They won't be the same every time. . Then in the future always weigh the powder on the scale using this standard weight.
Don't be lulled into a falses sense of secuity here and think you have no worries becasue you are only loading blanks. The pressures are still there, that's what is making the boom. Play safe.
One other note on booms. You may not think you have much of a boom...get out in front of your gun and listen you might be surpised how loud you are.
