Dick's buys guns for a price from Remington.
If the rifle is new, take it back and show them the problems you're having.
You're shooting factory ammunition? Decent quality stuff like Win/USA , Rem, or Fed American Eagle?
If you are shooting handloads, you likely have a very short OAL chamber, a good thing, but maybe your ammo needs more sizing?
Since you say you can check the headspace, what do your unfired rounds measure in your gauge and what do they measure once removed? Have you looked for debris under the extractor? Does the ejector spring actually function? Never know, seems obvious but....
If the rifle was purchased recently, take it back and get them to replace the gun, or sell it and buy one from another dealer. If you want a fine .223, look at the Tikka T3 varmint with the 1:8 twist barrel, shoot heavy bullets in that one which your remington can't digest because of the slow twist... Maybe you can work a swap to your advantage.
Good luck!