Stopping in possibly far too early to say it's not "3 Per 5 Mining Charges" for Blast drill. it's "Up to 3, for 5 or more". You previously had a tech that was "Up to 2, for 3 or more" So you'll get 1 chunk at 1 chare, 2 chunks at 3 charges, 3 chunks at 5 charges, and thats the most you can get per explosion (without more upgrades).
If you use blast drills on atlantum and use the thresher on the chunks you can get clay that way as well.
Stopping in possibly far too early to say it's not "3 Per 5 Mining Charges" for Blast drill. it's "Up to 3, for 5 or more". You previously had a tech that was "Up to 2, for 3 or more" So you'll get 1 chunk at 1 chare, 2 chunks at 3 charges, 3 chunks at 5 charges, and thats the most you can get per explosion (without more upgrades).