I need to preface this post with the fact that I'm far from a beginner to old or surplus powder. I've used lots of old powder, and I've seen powder go bad. I also know that there are some on here who are far more knowledgeable that myself about such matters.
Powder being a bit harder to find nowadays, it seems wise to pick it up when one can. I recently acquired an older 5lb tin of SR4756. It's mostly full, missing about a half pound. It looks and smells fine. Under magnification, I can't see any sign of deterioration or anything mixed in.
I've never used 4756 before, but see that it's a tad slower than Unique, so I decided to work up a load for .45 acp. I normally use 6.0 grains of Unique with a 230gr powder coated bullets, resulting in about 850fps.
I worked up to 7.0 grains of 4756, with the highest velocity being 800fps. Same gun, same day, same chronograph that clocked the Unique loads. They shot and functioned fine, just lower than expected velocity.
Any thoughts or comments from any gunpowder experts?