hhhhhheeeeeeeeeee!!

i just completed my first ar15!! picked up the lower receiver yesterday, started working on it asap. I had so much fun putting it together. the Lower Parts kit was easy compared to how i imagined..

Thanks Eisenkreuz and Ratters for much info!! Anyways, here it is:
Del-ton upper, stag arms lower ( hopefully it will darken with oil to match upper)
The only unfortunate.... one of those damn detent things sprung out and launched somewhere in my room... probably never to be found. so now i cant fully secure the rear take down pin until i get a new detent
Couple questions:
1) In my LPK picture, what is that circular ring thing for? pictured to the right of the hammer spring. (was left unused according to assembly guide)
2)With no magazine inserted, I am able to cock the gun and the charging handle will spring back forward... Ok normal. However, when a magazine is inserted, I bring back the charging handle BUT doesn't spring back forward. With the magazine inserted, the bolt catch is engaged. Is this normal? how yours is like as well??
3) I cannot switch the gun to SAFE when it is not cocked ( butable to go into safe when cocked.) Is this how its supposed to be??
My marlin 917 is like this, can't switch to safe when not cocked.
Thanks!!
well anyhow there it is!!