Spent shells, stacked. Long ones, short ones, double banded ones. I was right on February 27, 2008 and I am right today!
(Formerly) To judge for yourselves it is best to go to the official government site to see the images in the highest resolution possible. The best way to get there is to go to
http://www.dodmedia.osd.mil/ and put in the search term Ingersoll.
Two images will come up:
and a glancing view here at:
another significant view is DM-SD-02-03911 which is no longer current in the government archives but a copy is here:
In any of these images, click on the expanded view and scroll down to the lower right-hand corner. There you'll see what I take to be spent high-explosive casings but what Mr. Paisley contends are rolls of roofing-tar paper, or some other kind of rolled construction material.
The only collaborating evidence I found on the web was an antique example from a forestry archive at Yale University. It nonetheless provided me with some verification as to the scale and mass of a high-explosive shell.
Modular Propelling Charges