I just took my new build to the range and had some issues with it.  
It is a PSA "build"  I just slapped a lower half and upper half together.  Colt pistol lower and a 7.5 inch upper half.  Stock from PSA.  

I took it to the range and had issues with it failure to eject.  It would extract the spent shell just fine, but it would get caught in the action.  I even had one do a complete 180 and head into the chamber backwards.   It looked like the fresh round was causing some issues with the spent round.  I would have a failure and look at the actionand see a new cartridge and a spent casing.
The brass was charred on the outside as well.   I wonder if i need to change my buffer or something.  Any advice?

ASC mags or Metalform?

PSA. I think they are rebranded metalform

Will do. Once I figure out how. I think I need an account, can’t just post here right?

I had that exact same issue. The ejector was tweaked just a bit, not riding right up against the bolt like it should.

Bent it back with a little thumb pressure and it ran 100% percent afterwards.

And what ammo?  My PSA upper hates Federal 147gr flatnose (this is really unfortunate as I have 3 cases of it for suppressed fun).  

It eats 124gr white box Winchester like an animal.  I'm also using the metalform mags and for the longest time I thought I had some hinkey mags...

Ammo was WWB 115gr.  No issues with the ammo.

I had the same issue and fixed it by slightly bending the ejector inwards so it made better contact with the shell casing as the bolt moved rearward.
1500 rounds later and issue has not returned.