The phrase "powerful ammunition" refers to having strong arguments or evidence that can be used to support your views or win a debate or argument. Full definition
Where available, as it increasingly is, international law provides powerful ammunition for the enforcement of fundamental rights guarantees. (newlawjournal.co.uk)
It is powerful ammunition in a potential trade war. (fuw.ch)
No adventure is complete without dangerous enemies, so install turrets, craft powerful ammunition, and... BOOM! (gonintendo.com)