M4 shoots two bb's at a time sometimes?

Well, another reason I officially announced my m4 broken, was the fact that it kept shooting two bb's at a time...

It has a port in the cylinder, thats in the back, so a airsoft gun tech told me I have enough air to shoot bb's through a 410mm barrel..
What i'm not sure is if I am indeed having the vaccuum effect, though not 100% sure, it seems like bb's are falling out of the barrel when i point it down, and when i shoot, that two bbs are comming out at the same time...

Is it having the vacuum effect or what is going on? Is it the feeder? the magazines?

Most likely a issue with the bucking. And while your at it, get a new stronger spring.

Yeah check the bucking or maybe adjust your Hop-up. I've also had this happen with my KWA when using some Madbull BBs, they proved to be to small which was causing double feeding issues.

Shooting two at a time? Hows that a problem!!! Your gun is bad@ss now hahah.

Try cleaning the barrel! That happened with my M4 and I just cleaned it with the cloth strip/cleaning rod and it works fine now.