Barrel aligning tip
When you are installing the barrel, the pin on it that goes into the slot in the upper receiver will have a little play in it. If you don't have a way to hold it centered, when you tighten the barrel nut, it will go to the shooters left a tiny bit, just enough to put the shooters sights about 2 1/2 to 3 inches off at 35 yards when he is trying to zero. To keep this from happening, the bigger companies have a high dollar alignment tool to hold the barrel centered while the nut is torqued down. My solution is to put a toothpick on each side of the pin, then snip it off before i tighten the barrel nut. It isn't perfect, but it keeps the front sight post reasonably in alignment. Nowadays with more and more AR's using a freefloat hand guard with the rail on top, that isn't so much of an issue anymore, but I thought I would share the tip with anyone using old style front sight post.
"Democracy is two wolves and one sheep voting on what to have for dinner.
Liberty is the well-armed lamb contesting the vote." - Benjamin Franklin