I've now watched 3 separate clips. A C-Span clip, an ABC News clip, and some other random clip on Youtube don't know who it belongs to. Here they are:

Random one: https://www.youtube.com/watch?v=UIprRLYcteA&t=11s

ABC News: https://www.youtube.com/watch?v=xiNAly9CKSs

C-Span: https://www.youtube.com/watch?v=ZwvbQR887W0&t=8h12m15s

In the random one I only see/hear 10.

ABC News, I can't even tell they cut out and around and talk too much.

On C-Span I THINK I can hear 19, but at one point there is what seems like 30 seconds of silence between shots, and the video seems to cut weird during that time a few times so maybe the last two shots occurred during those glitches? (funny I was watching it for a while before then and no apparent glitches. the timing of these glitches are seeming less and less coincidental).

So here's what I can say for sure are differences:

1. The number of guns. In Trump's it was 4 guns present, 3 guns used 7 times each. In Biden's it was 3 guns present, 2 guns used (still unclear to me how many times).

2. The intervals. 3 seconds between shots for Trump. 9 seconds for Biden.

3. What the soldiers calling out the shots (not manning the guns) did BEFORE the salute. In Trump's there's a lot of pomp and procedure, including calling out the 21 gun salute so everyone can hear, and announcing at what intervals they would be shot (3 seconds). In Biden's there's no announcement beforehand. No explanation. Nothing said about intervals. They just yell once and the shooting starts. Not sure what all of that means, but it's what I've got for now.

*edit - maybe 4. Does the location matter? I don't think Trump's was at the cemetary. Have others in the past been there? Does that matter?