Ice

With a production cost of only ~.02$ per kilogram, ice is the cheapest projectile you can shoot.

Manufacture

Ice is generally cast (aka frozen) in molds made from PVC pipe the same size as the barrel. The specifics of this casting process vary, and the below is merely BLB's personal favorite:

* Cut numerous short segments of PVC pipe (DWV acceptable).
Lubricate the insides with petroleum jelly or grease.
* Arrange these in a metal pan of some sort.
* Fill the pan to about .5" with water, and place in freezer.
* Once this layer is frozen, take the pan out and fill the individual pipes with ice cubes,
and top off with cold water. (Using ice cubes prevents fractures forming in the ice)
* Replace in freezer
* Remove from freezer once frozen, and remove the pipe segments. Set these on the counter and
let sit ~30 minutes.
* Push the cylinders of ice out of the pipe segments, and use immediately or store in freezer.

Problems with manufacture

One of the major issues with ice is that it tends to form fractures, even when water mixed with ice cubes is used, when cast in large diameter or long pipe. This can be remedied by adding an impurity - sugar or salt works well - to the water. This impurity is not incorporated into the crystal structure of the ice, causing the concentration to increase until it becomes impossible for the ice to freeze.
Unfortunately, this decreases the strength of the ice.

Use and target performance

In theory, ice could be made to fit extremely well in the barrel, but in practice, it's not so simple. For some reason, the cast ice seems to be slightly too big to fit in the bore, and thus requires carefully controlled melting to get it to the right size. This typically results in a projectile a few hundredths undersize; some performance is lost, although this can be regained by using a chunk of foam as a sabot.

If the chunk of ice has fractures in it, it will often break up into two or more pieces, degrading accuracy.

Upon impact with:

• A twig, ice remains intact.
• A water filled milk jug, ice remains intact unless a fracture existed in the sample.
• A tree, ice tends to shatter into many small fragments unless the angle of impact was exceedingly shallow. Typically, no damage is done to the tree.
• A rock, ice tends to shatter into many small fragments.

Specifications

• Density: .917g/ml at 0 *C
• Tensile strength: ?
• Compressive strength: ?

See also

pycrete, ice's stronger sibling