An AR-15 such as a Colt 6920 has no firing pin spring. It just doesn't.
Therefore, one could logically deduce that you're looking at a different part or like someone mentioned a completely different bolt carrier design that has nothing to do with the style of your rifle.
I'll put it to you this way:
You mentioned that your rifle works fine, so don't even worry about it.
I've got a feeling this thread will get locked.

