The rare case where the primer ignites, but there are not enough gasses to force the bullet out of the barrel. If the round fired did not sound right, nor did it hit the target, stop and do not fire another round. A bullet may be lodged in the barrel and the firearm may burst if another round is fired. If possible, remove the bolt or open the action and inspect the barrel from the breech. If a bullet is in the breech, use a rod and push it out from the breech. Never push it back in from the muzzle. Clean the barrel before shooting again. …and wear your eye protection!