With ammo that is softer, made of gel and water, the answer to that question is varies.
The sensitivity of the impact varies from person to person. We compare the sensation to being snapped by a rubber band. Compared to paintball and airsoft, Gelly ball, gel blaster guns, or splat ball, has a far lesser impact.
A red mark may be left by an impact, especially one that occurs up close and on uncovered skin. Close-range combat frequently leaves small red marks on exposed skin or through thin or tight layers of clothing. These marks do not last long and the sting is very temporary. Most often younger kids are right back in the game after getting hit becuase it is mostly a shock not pain. Wearing thinker pants and sweatshirts will help reduce impact and we always suggest everyone bring those items. Layers can always be taken off if the player wants.