User blog comment:Master Moridin/A (Potentially Unnecessary) Explanation for Inconsistent Ammo Count/@comment-26397825-20151107053015/@comment-25396609-20151107054224

The pre loaded canisters look different, they have a meter on the side.

This is different than the wall tubes, if you look at the edge of the cyan you can see a fairly large gap between the viewport and the dust, same with the other colors just not as visible.

In addition, if they are powder form the walls would be more level rather than having the center portion elevated, which causes a gap where the powder could possibly leak out.