DB9 Slim Feeding issues

Hey Team,

First functional build that actually goes bang! The DB9 was a great project and I am excited to get started on a new one once I figure out some of the issues I'm having here.

The biggest thing is every so often a round will feed not into the chamber, but fall back behind the bolt. Seems to be happening with both OEM and Menendez mags. Any thoughts on what could be causing this and how to fix it?