found this interesting so i'm sharing.
just watched this
https://www.youtube.com/watch?v=KXfB59HenMA watch from 8:00
I didn't hear joerg mention the mass of the bolt. The crossbow is Excalibur Micro 335. specs :
http://smartarchery.com/excalibur-micro-355-review-top-rated-recurve-crossbow/http://www.bestcrossbowsource.com/excalibur-micro-335-review-in-field-recurve-cr...kinetic energy is 87-98fpe= 117-132J
@ 10:10 you can see it created a massive wound
The bolt has very similar diameter (blunt tip), Energy and momentum to a slingstone it differs only in velocity and mass.
132J= 0.5 * 0.1056kg * (50m/s)^2
a slingstone of 105grams and 50m/s has the same energy
sling stone momentum is : P=5.28kg*m/s
crossbow momentum for 350grain and 335fps (guessing since i dont know the bolt's mass): P= 102.108m/s* 0.02267kg= 2.314kg*m/s
Conclusion, the slingstone would have the same or bigger penetration.
the only argument against it is that higher velocities usually demonstrate better armor piercing but this is empirical not proved.