hi guys !
I upgraded this gbbr with a lot of parts, but the problem here is in the lower for sure. All the internal in the lower was upgraded almost with G&P parts (hammer, sear, bolt catch, anti-rotation link) and reinforcement springs and pins from element.
Since I changed all my parts, everything was fine except few small adjustments but nothing big enough to stress out. But lately, I was testing my m4 to see if it would be ready for my next game which is next Tuesday and :
*HERE is the problem :
AT SINGLE FIRE MODE, it shoots one bb when I press the trigger, and when I release it, it shoots again another bb, feels like it s burst haha.

anyways, in full auto it's all good and shoots like if there's no problem at all. I know it might just be a little stupid problem, but if someone knows or experienced this, plz let me know what to do.
till then, I ll try my best to get through this problem by myself
thx