GBBR Mag issue.

I ran my mags through the rifle to make sure everything is fine, since it has been a while.  About half way though the mags, they all started off gassing.  Another issue is double feeding/jamming right before this happens. 

Is this a Hop up issue or a mag or something else?  Everything is stock WE M4 (no NPAS).

Any help, please?

That is your bolt carrier group giving you. The problems, next time you try it, see where exactly your bolt closes, and if not closing completely, easy fix is to replace your BCG

Thank you!

I checked it, and the nozzle tip (that plastic spikey half circle) cracked and broke off - I found the cause of it too sadly.

A bb had disintegrated into little tiny pieces between the BCG and the Hop UP - caused and incomplete seal.

Should I get the $120 aluminum or replace with the $25 plastic one?

I would get both, one to replace the Current BCG, and one for a back up, now that is what I have been doing is carry a back up BCG and charging handle
 
The aluminum should not break, and would just crush the BB instead, that is what my Inokatsu does since it's a metal nozzle tip, just carry a small dental prick to dig out the broken BB so you can continue playing

Dental pick - great idea!

Thank you very much!

No problems