Sir:
Have you ever been to Gettysburg and walked the ground where Smith's Battery was positioned? Have you looked at any of the early photographs taken of this area of the battlefield? You might find this link of interest:
https://www.gettysburgdaily.com/gun...w-york-battery-return-to-the-valley-of-death/
Ask yourself these question:
How heavy does the trail of an artillery carriage weigh?
What size stones would you have needed to depress the tubes sufficiently?
Would the stones have been readily available?
Would the artillerymen have thought to do this in the midst of battle?
What would keep the canister rounds in the tubes if the angle was to great?
Interesting question and soldiers of all wars are well known for improvising. Perhaps this was done at a different Civil War battle. I look forward to hearing what others have to say. Thank you for asking the question.