A head, a heart and a tail
You ought to find me, so don't fail
After my tail, send my head
From some bullets, I fled?
To make things new, now use me
And so to do, then affix me
Take my heart and duplicate
Before my head, place it straight
Congrats, I was not very tall
But now, I'm nothing at all
Great, now my tail is my head. Horror!
Fortunately, you let the rest in order
It is quite a long time, you see
I'll understand if you don't wait for me.
Who am I?