That would be slower than all of those I listed at 2350 fps for 123 gr.
Shooter 1 would be around 460 yards and shooter 2 around 255
I didn’t take the time to do the exact math because it doesn’t matter.
I think your math is off.
The lag between bullet arrival and arrival of the sound wave would be very different.
Flight time for the bullet would be about .72 seconds for 400 yards. Time for sound arrival would be about 1.04 seconds. That would be a lag time of .32 seconds. Pretty close to the “shooter2” stated lag of .374. Speed of sound is approximate. It could be calculated much closer based on the current pressure and temperate in Las Vegas at the time of the shooting.