WE M&P Slide 'Sticks'

[mp5a4]

Hi, i recently got this WE Big Bird And it was functioning fine until today, when i pull the slide back the 'nozzle' doesn't go back every time and doesn't cock the hammer, when this 'nozzle' doesn't move back it also fouls the ejection port cover and prevents the slide from returning to its place.

This occurs when shooting also.

Any ideas? (I'll upload a video later)

 

[M_P]

Have you lubricated it etc?