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
Trump had 4 cannons. Biden had three cannons.
I guess you could sort of get confused about volleys and salutes. I’m not military.
Three volleys is for funerals and foreign visitors that sightsee for a few days. But a volley isn’t done with artillery.
https://en.m.wikipedia.org/wiki/Three-volley_salute
They're actually different things anon.