marushin m1 garand not ejecting mag ?

[b54gun]

Hi
I have a marushin m1 garand gbb , its blowing back nice and strong but on the last shot it wont eject the mag the bolt locks back on empty but just needs to go about 5mm more to eject the mag , when you pull the slide it moves nicely but the last little bit seems a little tight , so basically you shoot the bolt locks back on empty you just slightly pull the bolt a little more and then it ejects out ?
Ive stripped it down so many times think i can do it blinfolded now , everything is running smoothly and nice ,ive even put a weaker spring in the mag release button
Anyone had this before or know what it may be?