French practice during the period was to have only one caisson per piece accompany the gun company into action.
The other caissons would be with the parcs and would be moved forward to replace the ammunition caisson with the gun company in a rotation.
If we're talking only 1815, each 6-pounder would have three caissons, and each twelve pounder and howitzer would have five (for a 4-punder there would be two caissons, for an 8-pounder, three-the same as for a 6-pounder).
When emplaced, the piece's coffret would be placed on the gun limber, and that ammunition would be used to feed the piece, and it would be replenished from the caisson.
Depending on the terrain and tactical situation, the limbers could be in line behind their respective field pieces, and the caissons in a line behind them or they could be placed elsewhere close enough to keep supplying the pieces in the gunline.
Sincerely,
M
paints the Dogman from the Flintloque starter set.
