This depends on the material the door seal is made up of. Silicone rubber seals, commonly found on Sechrist™ brand chambers, do not require powdering. Seals made of other rubber materials, like those found on Perry™ chambers should be powdered only “as necessary” to prevent it from “sticking” to the door when opening / closing. A buildup of excess powder can result in air escaping past the door seal when the chamber is under pressure.