spez. This may be fake news. It seems like the interval between shots doesn't really matter and it's the total number of shots that matters. Also the total number of artillery guns doesn't matter either as long as 21 total shots are made. Presidents get 21 shots while others will get lesser number. For example, VPs or foreign dignitaries get 19 shots.
sauce. https://en.wikipedia.org/wiki/21-gun_salute#United_States
https://twitter.com/reaHJFarnsworth/status/1353482161962115072
https://www.youtube.com/watch?v=xiNAly9CKSs - Biden, seems like 3 guns and 10 second intervals is correct.
https://www.youtube.com/watch?v=eFX_7IR91Vk - Trump, 4 guns and 3 second interval
Based on this video, I heard only 17 cannon shots.
https://www.youtube.com/watch?v=ZwvbQR887W0&t=8h12m15s
Base on screen shots of the rounds magazine before and of the last scene I counted 19 missing rounds. Two are the right gunner's hands. Did Biden only get 17 gun salute?
According to this document:
https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/ARN20654_R600_25_Admin_FINAL.pdf
That's:
Interesting.