You can use my previously supplied Desmos plots and explanation to do this.
There’s no mystery here.
The speed of sound was 1152 fps.
If you have the (1) snik-report durations on a mic, and you know (2) the distance of the mic to the bullet at it’s point of closest approach to the mic, and you know (3) the distance from the shooter to the microphone.
THEN you can calculate the average velocity of the bullet with simple math.
If the shooter was Crooks on the roof, the numbers are:
(1) 220ms (1st shot) (MAIN MIC that Trump was speaking into)
(2) 1.07 ft
(3) 454 ft
The average velocity of the bullet was therefore 2622 fps.
You can use ballistics calculators to see what the implied muzzle velocity is for any particular brand and grain weight.
But it seems pretty clear to me, that given the barrel length, it was almost certainly a 70+ grain bullet.