hello while working on my gladiator 10an..i was replacing the mainspring with a nice nos part..after a few tries to with no luck..i wonder what the problem was..then i notice that the inside of the barrel , the catch that the out side of the spring hooks on too isn't as large as it should, well i compared to a 10ae barrel i had..and realize the problem...the inside of the barrel was snaped off, so the last coil of the mainspring couldn't hook on to the barrel...i never heard of this and now i will always know what to look for...always check everything and you too won't waste 10 mins for nothing..
Your still learning, It's best that you see these things the hard way, trial and error, now you will always check that as well. Just like a selfwinder I once worked on........it would take a full wind and become fully wound and stop winding. Took me a while before I figured out the safety was missing! Duh....