I think I might have something: A design that would weigh about 0.32 grams using the same material as 0.2gram BBs, with an estimated (calculated) ballistic coefficient of 0.148. Keeping speed to 410fps (125m/s) results in a muzzle energy level of 2.5 Joules. This ignores the possibility of minimum firing ranges, with higher energy levels (ie wherever pellet has only 2.5J).
Here's the ballistics I worked using the engine you showed (it has lower velocity limits, which is good). I set a zero at 50yards so one can aim COM and still hit only 6 inches high, to that point, for kicks.
And for comparison here's another calculator, but it has 500fps minimum:
Ballistic Coefficient: 0.148 G1 Bullet Weight: 5.00 gr
Diameter: 0.243 in
Muzzle Velocity: 500.0 ft/s Chronograph Distance: 10.0 ft
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yds) (in) (moa) (in) (moa) (ft/s) (none) (ft•lbs) (s) (in) (moa)
0 0.0 *** 0.0 *** 501.5 0.449 2.8 0.000 0.0 ***
10 -0.6 -6.0 0.0 0.0 497.1 0.445 2.7 0.060 0.0 0.0
20 -2.7 -12.7 0.0 0.0 492.8 0.441 2.7 0.121 0.0 0.0
30 -6.1 -19.5 0.0 0.0 488.5 0.438 2.6 0.182 0.0 0.0
40 -11.0 -26.4 0.0 0.0 484.3 0.434 2.6 0.244 0.0 0.0
50 -17.4 -33.3 0.0 0.0 480.1 0.430 2.6 0.306 0.0 0.0
60 -25.4 -40.3 0.0 0.0 475.9 0.426 2.5 0.369 0.0 0.0
70 -34.8 -47.5 0.0 0.0 471.8 0.423 2.5 0.432 0.0 0.0
80 -45.8 -54.7 0.0 0.0 467.7 0.419 2.4 0.496 0.0 0.0
90 -58.4 -62.0 0.0 0.0 463.7 0.415 2.4 0.560 0.0 0.0
100 -72.6 -69.3 0.0 0.0 459.7 0.412 2.3 0.625 0.0 0.0
110 -88.5 -76.8 0.0 0.0 455.7 0.408 2.3 0.691 0.0 0.0
120 -106.0 -84.4 0.0 0.0 451.8 0.405 2.3 0.757 0.0 0.0
130 -125.3 -92.0 0.0 0.0 447.9 0.401 2.2 0.824 0.0 0.0
140 -146.3 -99.8 0.0 0.0 444.0 0.398 2.2 0.891 0.0 0.0
150 -169.0 -107.6 0.0 0.0 440.2 0.394 2.2 0.959 0.0 0.0
The bad news, moulds costs between $2000 and $8000, so I'm going to need to do a lot of my own experimenting and research before committing to have a mould made. Damn, at those prices the design would have to be perfected, for sure.