Glad to hear it's feeding better. Sounds like it just needs to break in more. Use good ammo, Win white box at Walmart is good for practice.
I'd hang on to that "exploded" casing, maybe post a pic here too. Maybe take it where you bought the gun and ask them. Keep an eye on that, it's not normal if this is factory ammo. It could have fired while not fully chambered.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek