I don't crimp. The amount of bullet in the neck of almost any rifle cartridge will keep the bullet seated. I've fired literally Thousands and thousands of .223 reloads in AR's with NO issues with no crimp.
Now, some of my Long Range rifles that have a very high coefficient of drag, that is have a boat tailed bullet and a very long pointed tip, they sometimes don't get much of the bullet into the neck, in order to get the bullet near the lands of the rifling.. those long pointy BT bullets don't like to jump far to the lands. So these reloads are used in bolt action rifles that are single shot fed.
But, one thing that is critical with AR's and other auto loaders, is to resize the case. If you don't, it only takes one slightly too large a case to jamb the action.. and while at the bench shooting at paper this is not a huge deal, there are other instances where this could be a major problem and be deadly..