Saying 7625 has the same pressure curve has nothing at all to do with its ignition capabilities. You can put a pile of black down on a flat rock & throw a match in it & it'll go WHOOSH. Put a pile of 7625 down on that same rock & thow a match on it & the match'll burn out but the powder won't.
Black powder burns at essentially the same rate regardless of confinement, NO smokeless does. With smokeless the higher the pressure the faster it burns 7 the faster it burns the more pressure it produces, so while in a very limited range Black & 7625 can have virtually identical pressure curves, BUT, this does not hold true all the way across the board.
Hey, I'm not trying to stop anyone from using 7625 if it suits them. I decided about 30 yrs ago it did not suit my purposes. All I said was "BE CAREFUL" with it.
When it did let me down in the middle of a duck swamp it did manage to get everything out the bbl, just not with enough OOMPH to kill a well hit Duck. It was a Mallard Drake & this was pre lead ban. I was shoting a 1Ľoz load of #5 shot which according to DuPonts current data shoud have produced 7K psi, that's not even a pip-squeak 5K. He did come down but hit the water swimming. My son finished him with a 1oz load of 6's loaded with Unique from a 20ga. We checked him carefully when we dressed him & the #6's had penetrated well, the #5's were buried in the skin. I honestly don't know what made him fall, unless he just got off balance, the 5's had not done enough damage to hurt him much. All who insist on using slow powders at low pressures just be certain & make sure every shot empties the bbl, shame to ruin a good gun from a stuck charge, that's all I'm saying. There is plenty of evidence out there that slow powders in cold weather lose ballistics. This becomes even more notable when pressures are low to begin with.
