As stated, the spent case hitting the upper receiver defector is normal, and the defector is on the upper for when you are shooting the rifle south paw so the spent cases don't come back and tag you in the face.  As for solving the case dent problem off the defector if major enough since you intended to reload the brass, then a piece of sticky back Velcro Cloth side on the defector face will resolve such.


Now having stated that the spent case hitting the deflector is normal, what is not normal is the spent cases hitting the back edge of the ejection port window on the way out instead. To check for this problem, just pull the charging handle all the way back, and see where the face of the bolt stops against the back edge of the ejection port window.  The front face of the bolt should stop 1/8" to 1/4" in front of the back window edge.

If the bolt face is stopping flush with, or behind the back edge of the ejection port window, then the quick band aid is to just pull the buffer and spring, and drop the needed amount of quarters down the tube as end of tube shims to get the bolt face to stop at the correct relationship to the back window edge.  The best solution instead, face the  front of the tube so it can be threaded farther forward in the receiver when installed to achieve the correct relationship of the bolt face to the back edge of the ejection port window; while both the end of the tube kissing the center pin of the buffer retainer pin, and indexing for the butt stock correctly.

Clean the gun with CLP, including using a Chamber brush with CLP to clean the chamber as well.
The rifle parts come with a protective coating of grease, and this has to be removed before the rifle is fired to being with.


Also, CLP had a cleaning agent in it, so not only is it a lube, but a cleaner as well.

So the rifle bore itself, that is cleaned with a good copper solvent like Sweets copper solvent first, then the rest of the rifle is first cleaned with CLP, then the fouled CLP removed and a fresh coat of CLP to the upper receiver bearing areas.

If you need a good source of CLP, then the large spray can of BreakfreeCLP is just the ticket (under $10 at Walmart).

Note again on the barrel, start with the sweets to clean just the barrel bore (sweets will remove the copper fouling in the bore without a lot of needed scrubbing), run a couple of dry paths down the bore and out the muzzle to get the Sweets out, then CLP and chamber brush to clean the chamber, followed by that fouling pushed down the bore and out the muzzle with dry patches as well (Q tips to clean the barrel extension void).  Although the chamber and bore will seem dry, there is enough CLP still on the surfaces for short term storage of the barrel to prevent rust.   As for one the barrel has been cleaned, then you can attack the rest of the rifle to clean it first, then once that mess has been cleaned out, then a fresh layer of CLP on the upper receiver bearing areas to complete the cleaning and have the rifle ready to run.