Ar 15 pushing bullets back

Sine the OP is new to reloading I will mention one thing. He is resizing with Imperial sizing wax and may be putting wax on the inside of the case neck. If so, its a good idea to run run them back through the cleaning cycle to remove it prior to dropping powder and seating bullets.

That’s debatable. If there’s a lot of it, sure. But most if it should be wiped out by the expander ball or mandrel, and a thin layer of wax in the neck can prevent cold welding.

Really clean necks and really clean bullets are a great combination for producing cold welding if your ammo sits for a while before use.

But yeah, if he’s got a bunch of lube in there it could definitely contribute to bullets slipping in the necks.