Well, this was the first time I've seen that it should be larger than 10-1/4". So... But the man's opinion does carry some weight if he was an armorer. Yet if a lot of peoples carbines are working and their spring is 10-1/4", it's probably nothing to worry about. But all I know is when I tore mine down, it was only 10. It was a long time ago, but I'm pretty sure I ordered it from fulton. And it didn't see so many rounds that it should be worn down. Not to my recollection.