You are correct. I've made an error in my formula: I switched around the exponents 0,75 and 0,7 which lead to wrong values.
The correct velocities, calculated assuming K=2400, are these:
- V(m/s) Range(m)
- 757 100
- 716 300
- 684 500
- 601 1000
- 531 1500
Still, no matter what K we use, those two never align. It's probably worth to check if the terminal velocities of other german guns are (in)correct as well.