1. Ratchet Bomb has an activated ability, not a triggered ability.
2. That activated ability has its costs paid before your opponent gets priority to respond. One of those costs is to sacrifice it. Therefore, it's no longer a legal target for Clockspinning
, so this play is illegal.
If, however, they had targetted an untapped Ratchet Bomb that had 4 counters on it, then the Bomb could be activated in response, and force all nonland permanents with CMC of 4 to be destroyed. The Clockspinning would then fizzle for having an illegal target.
In short, they're pretty much damned if they do, damned if they don't.