the second bullet (the faster one) will impact well above the slower bullet on the berm. The point is not to hit the same spot, but to see if the second bullet can be made to impact first. Therefore, no sight adjustment would be necessary.
After sleeping on this idea, it occurrs to me to be dang sure that the first bullet (the slow one) has actually exited the barrel before firing the second one. It's not that I'm fast enough to fire the second bullet with the first one still moving down the barrel, of course, but it will be important to make sure that the first bullet doesn't lodge in the barrel before the second one is fired. I've made that mistake once...
Reportedly, the military practices this with howitzers, aiming the first shot real high for a long hang time. However, their target distance is considerably longer...
KN, we actually discussed trying to hit the first bullet with the second. However, our range rules prohibit us from shooting at metal targets.
Test results to be posted.
The Blade