I'll take a stab at this. In this photo:
The projectiles are about 12px high, which corresponds to our known bore width of 4.2 inches (
link ). They are about 31px long, which works out to 10.85 inches.
That picture shows the rammers as well, but they're a little trickier, because the shells hide some of their length. We know the barrel band of the Parrot is 19" long, so that's a good comparator.
Here's another image, of re-enactors:
Say the rod the rightmost gunner is holding is 6' high, that would make the rammers on the ground 12.4'
FWIW, the bore depth of the Parrott was 121" or just over 10 feet, which makes me think the rammers must have been a little longer than 12.4' -- although this video now makes me think that I'm pretty close: YouTube link
bases them up.
