Shotshell performance is based on powder burn. Chemical reactions are highly dependent on temperature. Propellants, such as nitro powder, are also dependent on pressure for burn rate. The initial cold temperature must be overcome to raise the temperature and pressure sufficintly to achieve normal burn rate. That itty bitty fraction of a second while the powder jump starts itself can sometimes be sensed. A blooper occurs when the powder can't develop enough pressure to get up to normal burn rate before the shot charge moves and increases the combustion chamber volume.
