It was really that common for an officer to not now the difference between a cannon amd musket by name? Huh thats an odd one.
Unless maybe some artillery officers refered to their field guns as muskets or something?
There where only about 1000 officers in the US regular army when the war broke out.
At the Battle of Shiloh only the union Divisions where fully commanded by professional officers, at the regimental level and company level all officers where men who until the outbreak of war, had been civilians.
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One example of counting.
On a list of stuff picked up at Gettysburg after the battle and moved to the Washington arsenal, most officers involved with the collecting and counting used the name "muskets" for the infantry firearm they pick up.
So 800 muskets, another give 339 muskets, 425 muskets...
This have to be both smoothbore muskets and rifle muskets of all models and versions.
(Since we are talking 20.000+ weapons and as such they must represent a wide selection of arms in sue by both sides during the battle)
Some just list "accouterments."
Other list Cartridgeboxes, belts, plates and cap-punches.
One officer lists
10 rifles,
10 saber-belts
2 Caissons and limbers.
Do rifles mean rifled cannons or small arms?
Since he also list 11 Bayonets I guess we are talking a small arm.
The next officer list 2
"Guns-rifled"
Since he is from an artillery battery and also list a gun-carriages and 2 limbers I guess his "guns-rifled" is two cannon.
But we cant be sure. Had he clearly written "2x 12pound Napoleon" or similar, it would have been clear.
And the are plenty of other issues with this list.