https://www.ar15.com/forums/AR-15/New-N ... 15-754694/Check out the thread above, I modified my lower the same way.
Basically, remove the ejector and grind down the height of the feed ramp. A pretty easy task with a belt or wheel sander.
Also, regarding mags...Manticore mags will run without modification. PSA mags will also work but need to be cut/grinded (somewhat aggressively) at the top edges so it will clear the carrier.
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