WE Glock 18c Semi Issues
 

Ok ever since I bought this gun (refurbished it said) When on Auto, The gun functions perfectly. Flick it to semi-auto and it will shoot bursts or auto about 90% of the time. Then it seems to me like when the mag gets to about a 1/4 empty it will fire semi a couple times then go off on its random angry G18c tangent again. I have done the whole search thing and can't find anything similar. Anyone have any ideas?

EDIT: fixed... simple over lubing. Thanks anyways.