Where did we get that information? From 40 years of reading about such things. Can we give you a shortcut for all that info? No. What we can do is to give you a reason why we can remember these stats. And please remember we are cannon makers, not professional researchers or research consultants. So, as for the 25 lbs of powder or the 250 lb. shell or the range in yards, you can find those on any one of a half dozen good quality artillery sites on the net.
The 1,200 fps. can be found on the net, but, if we had the time, it would be easier for us to go to 4 or 5 of the 70 or so books on artillery that we have collected in the past 37 years. We remember this because it is a part of an overall scheme which keeps the tables of fire essentially the same for every Parrott rifle. The origin of that idea is unknown to us, but you can imagine how popular this system was in Army circles! By actual range testing, the powder charges were adjusted (3.25, 10, 16 and 25 lbs. of BP) to allow a single, specific, elevation to obtain the same range with the 30, 100, 200 or 300 pounder Parrott rifle. Don't know if this applied to the 10 pdr. field gun or not. The muzzle velocity was very close to the same at 1,200 to 1,300 fps among these big rifles.
The 440 lb. cored shot for the Rodman Gun obtained an astounding muzzle velocity of 1750 fps with a 60 pound charge. We remember this because it's so unusual for a huge gun to have this velocity level. Also there was an article in the London Times of the 1860s or 70s which described the terrible effect on a 10" thick armored target of the best wrought iron plates. "It simply vanished", astounded observers said. Actually, only about half of the 4 ton target disappeared only to be found scattered like leaves in the wind at the 100 yards butts. The target was at 25 yards. The 24 pdr. seige gun will do it with 10 lb. charges, but over that size the vel. numbers usually go down. As for the formula for finding muzzle energy, regarding the 5 1/2 million ft. lbs., we use the one that we both learned in Gunsmith School 31 years ago and it is:
MASS (expressed in grains, 437.5 grains per oz.) X VELOCITY2 (expressed as fps.)
MUZZLE ENERGY = ____________________________________________________________________
450,400 (reflects the new figure revealed by GGaskill)
After checking my old gunsmith notebook. I find I made an error here and the denominator of 450,800 was not accurate and that 31 years ago we were taught to use 450,240 which George also mentioned.
Regards,
Tracy and Mike
