Indeed, these are samples, and more precisely - 'Blutonium Boy Hardstyle/Hardcore Samples 2007' - something like that. Most of these kicks sounded quite poor at the time, so I had to redo them, strengthen them, turn them up and create something of my own from the base, but really - a sample is a sample. I have to create my kick sometime. : D
POWER!
https://soundcloud.com/mckinleymuzyka/sets/danny-toples-hardbass-attack-2019