Usually when it's cooler outside and you've had the guns out for some time, they aclimate to the temperature outside. You bring them inside in the warmer environment and they will sweat until the metal aclimates to the inside temperature and the condensation evaporates. NEVER bring the guns in from the cold and put them in a gun case.They WILL begin to rust if you don't let it dry and then oil/silicone treatbefore putting them up.