Some synthetic stocks can indeed move slightly when exposed to heat,such as when they are left in the sun on a hot day.They are however quite stable in the temperatures that most of us encounter while hunting big game.The stocks effected are the injection moulded plastic stocks that are common on factory rifles.However the higher quality synthetic stocks like mcmillan,h-s precision and rimrock,are extremely stable under all conditions of temperature and humidity that you would ever hunt under,much more stable than any wood or laminate for that matter.