With a production cost of only ~.02$ per kilogram, not counting wood/paper pulp, pycrete (also spelled pykrete) is the one of the cheapest projectiles you can shoot, and is much stronger than regular ice.
The pycrete pulp is traditionally produced by mixing sawdust/wood pulp/mulch with water at 14% by weight, although mixing it at a higher percentage by mass seems to produce a more robust material. Personally, BLB prefers using paper pulp; newspapers are plentiful and it's less messy.
To make pycrete pulp using paper, simply soak the paper in water for a bit, and then shred with a blender or a mixer. Add as much water as the paper pulp will hold, or a bit less.
Pycrete is generally cast (aka frozen) in molds made from PVC pipe the same size as the barrel. Due to the water-absorbing qualities of paper pulp, the casting process can be simplified a bit. Using wood pulp, you'll have to refer to the casting process used here. 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 individual pipes with the pycrete pulp. Add a bit more water to make sure it's saturated.
- Place 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.
Use and target performance
In theory, pycrete could be made to fit extremely well in the barrel, but in practice, it's not so simple. For some reason, the cast slugs seem to be slightly too big to fit in the bore, and thus requires carefully controlled melting to get it to the right size. With pycrete, due to its lower thermal conductivity, this is easier done than ice and tighter tolerances result.
For the true velocity connoisseur, the bit of lost speed can be regained by using a chunk of foam as a sabot.
Upon impact with:
- A twig, paper-pulp pycrete remains intact.
- A water filled milk jug, pycrete remains intact.
- A tree, pycrete remains intact. With grazing blows, some damage to the bark may occur.
- A rock, pycrete tends to shatter into several fragments, unless the impact was shallow.
- Density: est. 1.0g/ml at 0 *C
- Tensile strength: ~1000 psi from memory
- Compressive strength: 3000 psi claimed