The reason why is really simple, yet hard to explain. Real grenades use explosives (duh) to let the shrapnel fly. No one is so stupid to put 20 mil HE-frags in his knex guns, (even though someone really tried to!), so we have to resort to other measures. So that is why you basically get three types of knex grenades. 1: These grenades are poorly built together so they will fall apart when they fall on the ground. This means some of them fire a lot of shrapnel, and most are easy to make and have a low piece count, but there is hardly any power; they just collapse. This makes them the most useless knex grenade of all. Examples: https://www.instructables.com/id/Knex_Grenade_17/,https://www.instructables.com/id/Knex_grenade_14/,https://www.instructables.com/id/Small-Knex-Grenade/2: These grenades are much like the first one, but they have rubber bands so they don't just collapse. They still have poor power compared to real ones or other knex guns. Example: https://www.instructables.com/id/KNEX-GRENADE_3/,https://www.instructables.com/id/knex-easiest-grenades/3: These grenades have a more complicated design, meaning they use more pieces, which is a significant disadvantage if you need to use multiple grenades. However, they pack a much bigger punch, which makes them possibly the best on the site. Most of them also have securities so they don't blow up in your pocket. But they only fire in one direction! Example: https://www.instructables.com/id/Knex-Grenade_8/,https://www.instructables.com/id/Project-X4-XPLODER-Mini-Knex-Hand-Grenade/,https://www.instructables.com/id/The-D-Frag-knex-grenade/So all of these grenades have things real grenades don't have, and thats why there are no good ones. If you really need a good knex grenade, use either the D-frag, the IAC war bomb, or the X4.