FN1910

Part 115 is the extractor that falls out and is easily lost. You will either need to see a exploded drawing or an actual gun to see it because it is a very small part that just fits into a slot with nothing to keep it in. No one seems to know the real purpose of it but usually it is said to assist with ejecting the shell when the magazine is empty.

With it missing it usually causes no problems except sometimes the last round of a magazine will not be ejected properly. Or at least is my understanding.