I owened a KJW M4 and own for 2 years a G39 WE as my main gun. Below to 5 celsius they don't stand a chance against AEG. I shoot only semi. After 8-10 shot I have big fps drop and gaz leak in the chamber.
I can maybe get a mag if I keep the mag next to my balls for warming up. that ' why I have AEG as back up for spring and fall.
Otherwise it's a great platform for milsim lovers... but not for performance and trouble who come with.
We will find a way.