Since we’re not looking at a “photo-stopped” bullet, it would be more accurate to take another of his [new 50] cartridges and fire it through a screen that measures such velocities across that known distance.
https://www.sierrabullets.com/exterior-ballistics/2-3-1-initial-velocity-and-final-velocity-method/
I am saying this as a retired government “Forensic Ballistics” examiner of 27 years, who never was required to determine bullet velocities for the courtroom.
I just heard (Kuhner-WRKO Boston) that the SS was inside the building where the shooter was located on the roof!
The bullet discussed in your link had a velocity of about 2500 fps when it was about 100 yards downrange. Assuming the one in the Trump photo is moving at a similar speed, then it would be traveling 2.5 feet per millisecond. Judging by the length of the blur, I would say it traveled about 1 foot during the camera exposure. Or maybe a little longer if its path is foreshortened by the camera being off-axis from true broadside. So maybe we say it traveled about 2 feet, or to make the math simple we can say 2.5 ft.
Given this, the camera’s exposure time would’ve been 1/1000 of a second, which seemed unrealistically short when I was thinking about it the other day. But after doing a little poking around, it’s really not. Many consumer cameras can do exposures as short as 1/8000 of a second, and when shooting a bright outdoor scene 1/1000 is probably not that uncommon.
So I’m going to flip flop and say the blur in that photo probably is the bullet.
I only wanted to check velocity to see if it is consistant with 223/5.56 at that distance, and maybe with or without a supressor.
Or, slower, like a 22LR.
Or some other round, like from a different rifle of diffenent caliber or different distance (like from a 2nd shooter).
Such an analysis would confirm the narrative, or ... not, raising a couple of more questions.