SOOOOOooooo. Me and a few of my friends were discussing the use of bombs/powder horns & hewards hireling armor to make a suicide vest? would this work? the principle is bombs weigh 1lb and you can store 20 in one pouch running the fuses to one fuse that runs out of the pouches.

RAW, this idea falls flat because bombs are limited in their power. Normally you can't do anything like detonating 20 bombs at once from one NPC.

However, GMs can make anything. Say, a bomb that is the equivalent of a delayed blast fireball that is bound the suicide vest and moves with it while the rounds go by. Or an NPC that can detonate 20 bombs at once from one NPC action. Players can't.

The simplest bomb is the use of an entire necklace of Fireballs at once.  (16d6, 20ft radius)

Or the use of the various gunpowder things, such as multiple pouches of Blasting Powder from Wildemonte  (10d6 20ft radius max)

Homebrew it. Officially, it would likely just stack up damage in the small area of effect, but by merely saying that it deals up to 1/3 of the theoretical damage less (i.e. 12d6 --> 8d6), to represent diminishing returns makes it not an OHKO on the boss.