The video gets some core Minecraft 1.21 mechanics right, but it also makes speculative or unsupported claims about world structure counts and a 129-account vault exploit.
Claim-by-claim breakdown
Accurate (97% confidence): Heavy cores are obtained from ominous vaults in trial chambers, and the mace is crafted from a heavy core and a breeze rod. Minecraft’s official 1.21 notes say ominous vaults can drop Heavy Core, and the mace is crafted with a Heavy Core and a Breeze Rod.
Accurate (96% confidence): A player cannot open the same vault again after personally unlocking it once. Mojang says vaults can be unlocked by multiple players, but after a player has unlocked a vault, they cannot personally unlock that vault again.
Accurate (79% confidence): Ominous vaults have about a 7.5% chance to drop a heavy core. Multiple Minecraft feedback posts discussing the 1.21 loot table reference a 7.5% heavy core chance for ominous vaults.
Unsupported (91% confidence): There are about 600,000 trial chambers in a Minecraft world, each with six to seven ominous vaults. Official Minecraft sources describe trial chambers as procedurally generated, but do not give a fixed total like 600,000 per world.
Accurate (83% confidence): Using 600,000 chambers, six to seven vaults each, and a 7.5% heavy core chance implies roughly 270,000 to 315,000 maces per world. The calculation is mathematically consistent: 600,000 × 6 × 7.5% = 270,000 and 600,000 × 7 × 7.5% = 315,000, but the inputs are not established by official sources.
Unsupported (95% confidence): A glitch lets 129 Minecraft accounts repeatedly reopen the same vault, making maces effectively infinite. Official Minecraft notes say vaults can be unlocked by an unlimited number of players, but I did not find official confirmation of a 129-account reset glitch. Community discussion mentions a 128-player tracking limit, but that is not a…
Unsupported (86% confidence): If one player spent 87,000 hours breaking vaults, they could destroy every vault in a world and make heavy cores unobtainable. I found no authoritative source supporting the 87,000-hour figure or the idea that vault destruction can make heavy cores globally unobtainable in the way the video claims.