I understand if you have an autoinjector, you _can't_ do this, but this is how I was trained to give injections as an EMT-B (and paramedic training provided by the Army, as I was an Army medic).

It was common practice at some point, and keeps being taught, but it's no longer recommended even for IM by most medical associations (unless your injection site is considered high risk; but that pretty much is never the case for SubQ 4-6mm with 4-6mm needles).

I went down this rabbit hole after being handed a 100 pack of insulin needles and an estradiol vial with zero instruction - seemed irresponsible at first, but it turns out it's pretty hard to mess up.

This is incorrect, always do this. Its called aspiration and it ensures you are not in a vein or artery.

It's no longer recommended by most medical associations or the WHO.

https://www.cmh.edu/siteassets/media-documents-for-depts-sec...

SubQ has an even lesser risk of hitting a blood vessel.