The true boom stick
Incorrect, these were developed in Norway by Nammo, several years ago. Pretty cool stuff. The US military did away with concussion grenades back in the 70s, they were basically a charge wrapped in asbestos. Ever since they pulled them we've made do with frags, which end up hurting friendlies.
One unit is standard concussion effect, puts people on the ground. Connect two and it puts people in body bags. Three makes it an anti-structure weapon. But no, no infinite stacking I'm pretty sure, even though that would make one hell of a bangalore torpedo, yikes.