Funny,
We put a rifle together for my friend last night (Not an AX556). The billet upper was pushing his bolt-catch OUT and he couldn't charge his bolt at all either. Since we had extra bolt catches, we replaced it with one that had no paddle and everything worked perfectly.
So, my thought is that it's a bolt-catch issue
Ask AX556 if they will send you another catch and just take material off the paddle until it fits. Simplest and cheapest solution.