[blackfoot1]

The bit sticking out the bottom of the trigger unit (infront of the trigger), is the spring guide stopper.
Slide it down and see if the bolt goes fully home.
And no, I don't think the cracks are what's causing the bolt jam... Still not good though.

 

[blackfoot1]

I'm pretty sure you've got the s/g stopper in back to front (in the pic above). I know it won't fix your problem, but I thought I'd point it out anyway.