jackssmirkingrevenge wrote:The projectile must be going fast enough to penetrate the target medium without giving it time to deform and absorb the blow.
This is an important point, and it's why my AP dart designs are deliberately being pushed to about 270 m/s (about as fast as moderately practical for a pneumatic), in order to try and minimise the target's absorption of a hit.
Similarly, more velocity reduces the deformation of the projectile - which is why a 90 m/s paintball can be flattened against sturdy card, but a 300 m/s one can go through intact.
However, in this case, due to relative projectile and target hardnesses, we can probably say that the issue is not so much projectile deformation as the projectile being annihilated. The energy is not going effectively into the target, it's going into the BB.
As something of an imaginative aid, consider a semi-elastic collision between two masses.
Looking at it as such, a projectile really wants to be more massive than however much it's got to punch through, else it's suffering a large change in kinetic energy, a lot of which will go into its own deformation.
In other words, the sectional density of the projectile should be higher than that of the target. You can get away with less SD if you add enough velocity, or with more SD, less velocity.
But you shouldn't rule out either. Both sectional density and velocity are needed, and there'll be a sweet spot of projectile mass where both velocity and SD are high enough. Too fast, and there won't be the SD to be efficient. Too heavy, and there won't be the velocity to be efficient.
How fast is velocity enough, and how massive is SD enough will vary with each target of course. Cheese isn't too fussy either way. Steel plate is quite picky about what will make it through, particularly as thickness increases.I got quite fanatical about the subject of efficient penetrators in the early stages of designing the AP darts, so I do have a few ideas on the matter.
Anyway, as DYI's BBs are likely already doing 1300 m/s or so, it's unlikely that practical increases to their velocity will be improvement enough.
With a heavier, slower projectile, the increase in SD might give it the edge.
I do have amongst my arsenal of ideas something that would get a 0.3g BB up well into hypersonic velocities (if I ever built it), but that's another whole ballpark.