How would the chalk be ejected from the front of a rifled projectile?
After thinking about this necessary action, I had thought that a reverse Parrot Percussion Fuze style striker could be machined and loaded into the chalk hole drilled in the nose. The open end of this closed tube would be facing toward the nose of the projo. Or you could load a loose-fitting 54 cal. lead ball first and then put the chalk in. However to be responsible at the range, you would also need to drill a hole across the projectile near the tip for a 3/16" hardened steel dowel pin which would be installed
after either of those loose-fitting powder expellers were in place. This safety measure would prevent pieces from flying off at unpredictable angles upon impact.
Thank goodness for Rayfan87!! His suggestion is much better in that it doesn't require machining parts, drilling holes or using other associated parts or assemblies. His idea is simple (KISS principle), safe and easy to make. Here is how we would implement it. Buy a small rocket nose cone at the hobby store, cut to an appropriate length (to fit on top of your flat nose bolt (like our Brooke projo), spray it with two coats of clear acrylic spray, allow to dry. Cover with dental mold silicone rubber (we have it on hand at all times to make Chamber molds before rifling a tube). The resulting simple mold is sturdy enough to make these chalk, bolt-ogives, (mix the chalk with 5% by weight dexetrin for bonding and wet the mixture slightly to consistency of Play-Dough and gently pack into the mold), let dry. Make five such molds with the same coated, wood cone if you have lots of bolts to fire. These chalk bullet tips are very fragile, so spray them with 3 coats of clear acrylic spray to form a plastic shell around them. Epoxy to top of your zinc, lead or steel bolt. Carefully align.
Needless to say, these will release their chalk dust instantly as impact occurs.
Great idea, Rayfan87; we will do ours this way! Hey, Bonus; no flying parts on impact, except lightweight wood splinters!
FURTHER KISS simplification: Buy a bag of those oversize sidewalk chalks. Using your mini-lathe, turn the nose ogive, flip and face off the other end square. That's it!! No lathe? Use a piece of 100 grit sandpaper on a flat surface and shape by eye. You can detect a angular divergence of only 1/4 degree by eye. Remember, a 1 deg. angle diverges a full .0175" at only 1" distance! Spray with clear acrylic for extra strength.
Mike and Tracy
P.S. I think Artilleryman beat me to it.