Reporting for duty with some noob questions

Just got my first AR put together. Sorry to deny you all my feet pic. Full ambi PWS lower (I’m wrong handed) with bcm 16” upper. First question: I’m about 500 rounds in, it seems my shells are catching on the metal extrusion behind the ejection port (chipping the paint). Does this signify my gun in under/over gassed or is this normal? The buffer is also bcm. Second question, I’m discovering the aimpoint duty rds has some funky mounting height, if I want to add a magnifier down the line how difficult will it be to find something the correct height? And third question, should I wait to get more acquainted with the gun before adding a can or just get one right away? Thanks for answering my dumb questions!

Just got my first AR put together. Sorry to deny you all my feet pic. Full ambi PWS lower (I’m wrong handed) with bcm 16” upper. First question: I’m about 500 rounds in, it seems my shells are catching on the metal extrusion behind the ejection port (chipping the paint). Does this signify my gun in under/over gassed or is this normal? The buffer is also bcm. Second question, I’m discovering the aimpoint duty rds has some funky mounting height, if I want to add a magnifier down the line how difficult will it be to find something the correct height? And third question, should I wait to get more acquainted with the gun before adding a can or just get one right away? Thanks for answering my dumb questions!