My copy has a 1975 copyright date, printed around 1987.
The part of the book I find most valuable is the last 50 pages of Black Powder ballistics. There's discussion of terms like mid-path, bullet path, ballistic coefficient, etc. And then there are extensive tables. The tables cover muzzle velocities typically from 2300 down to 1400 fps, and projectiles from .350RB up to .562RB and .575 Minie. For a given projectile and muzzle velocity you can see where the ball will hit, and with what energy, out to 300 yds. E.g. .445 roundball, 1900 fps mv, if sighted in at 50 yds, would hit 3.87" low at 100 yds, 40 inches low at 200, etc, or would drift 5.53 " at 100 yds with a 5mph crosswind. They don't cover every projectile - there is a table for .445RB, but not .440, so you have to take it for granted that the two balls' trajectories are 'close enough for government work.'
In the front of the book, there are about 67 pages of general articles which would likely be mostly of interest to newcomers to the sport (how flintlocks and caplocks work, bullet casting, cleaning your firearm, shooting the revolver, etc). There are 13 pages of revolver loading data - caliber with roundball or conical of this weight with barrel length with powder charge yields this much muzzle velocity and muzzle energy. A chronograph would give you better data for your particular gun and today's manufactured powder. Pages 82 through 143 are Rifle and musket loading data and give similar info as for the revolver section. They give you an idea about load performance, but I'd rather have chronograph data for my rifle and not rely on data generated 25 years ago.
The right software and a good chronograph would give you as good or better trajectory info than you'll get from the BP Handbook, but if my copy of the handbook were to disappear, I'd still probably replace it with another first edition just because it's a handy reference.
