MP9 Misfiring

[JinxDuh]

Picked up an mp9 with a broken disconnecter, replaced it with a Wii-Tech steel one. I have 5 mags, all of them do the same thing. 
 

It’ll fire the first 4/5 bb’s, then it’ll dry fire turning the gun into essentially a bolt action. I noticed that if I remove the bolt assembly and reinsert it some times it’ll go through two whole mags and then the third would do the same as above, fire a few bb’s and then dry fire. 
 

Mp9 is completely new to me, so I’m unsure of what to check. The nozzle seems fine, the feed arm isn’t snapped or broken. Unsure what else to check?!

[hitmanNo2]

Are the mags loaded "properly" i.e. neatly double stacked? I seem to recall MP9s can be picky with feeding unless mags are loaded like this. Even down to which side of the follower is touching the first BB.

[JinxDuh]

Just now, hitmanNo2 said:

Are the mags loaded "properly" i.e. neatly double stacked? I seem to recall MP9s can be picky with feeding unless mags are loaded like this. Even down to which side of the follower is touching the first BB.

Yeah, I followed Jaeger Precisions video of loading the first bb on the left side, does the same all the way. 

[JinxDuh]

Took a slow motion video and you can see the issue. The nozzle returns fine for the first few shots, and then the nozzle and bolt only “half move”

This is how the bb’s are stacked, with fresh green gas