I really don't understand, why no one has done this before.
Methods and explanation[]
After Kars cut the bullets, they all started to diverge AT THE SAME TIME (Kakyoin reference =). The anime also shows this. And also, that he deals one blow to each bullet. Based on this, there are two calculation options:
1) Bullets are static for Kars, therefore they diverge simultaneously.
2) Kars inflicted every slash while the last bullet on the frame caught up with the first bullet, since he managed to inflict one blow for each.
Let's start.
Second method[]
According to Stroheim, the bullets of the machine gun are 30 mm.

Distance between first and last bullet:
3 / 18 = 0,1666666666 cm one pixel.
0,16666666666 × 164 = 27,3333333322 cm.
Timeframe:
Most of all, the German MK 108 machine gun suits Stroheim's prototype machine gun. The calibers of its bullets are almost ideal for our situation (30 × 90 mm).
Bullet speed - 522.5 m/s.
0,273333333322 / 522,5 = 0,00052312599 seconds.
I don't know how to find the distance traveled by Kars's hands. Considering that Kars is a very tall character, even compared to Joseph, his height must be at least 2.1 meters. I will assume that one hit by Kars travels 1.5 meters. The total number of strokes is 11. This means that the distance covered is 16.5 meters.
Speed:
16,5 / 0,00052312599 = 31 541,1589472 m/s.
92,7681145506 mach, High Hypersonic+.
First method[]
Bullets are static, I will assume that they only went one centimeter.
Timeframe:
0,01 / 522,5 = 0,00001913875 seconds.
Speed:
16,5 / 0,00001913875 = 862 125,269414 m/s.
2535,6625571 mach, Massively Hypersonic+.
Results[]
- Second method = 92,7 mach (High Hypersonic+)
- First method = 2535,6625571 mach (Massively Hypersonic+)
If the second method is accepted, then due to the fact, that this is the upper end of High Hypersonic+, Ultimate Kars must be registered in the MHS, as its stats should have increased significantly, at least enough to become 1.07 times faster.