I bought a 1799 dollar in an NGC holder but the coin moves around a lot inside of the holder and I am afraid it could get damaged. I sent the coin back to be reholdered but I'm still having the same problem. Are large coins more snug inside of a PCGS holder and would therefore prevent movement? Has anyone had luck reholdering an NGC coin in a PCGS holder to prevent movement of the coin? To me the small prongs inside of an NGC holder look less secure.
Interesting. While I can't answer your question, I'd call NGC and let them know this situation and ask if they had different sized core prongs. See if they'd be willing to redo it at no cost. How loose is it? Can you just give a light twist and it moves or does it take a harder jolt? Sometimes a planchet isn't perfectly round and the fourth prong isn't in good contact. I had an ancient come back with no prongs, just a clear center. Maybe that would be an option.
Do you have pictures? If it's a low grade coin it could just be it doesn't fit well in a standard large dollar holder because of wear. Like when an AG wheat cent doesn't fit snug in a coin folder.
Over time I think all coins of all sizes move in their slabs. Since the slabs are plastic they may shrink or expand over time and the condition they were stored under adds to the problem you’re having.