What can you tell me about this upper?

[cneider]

This is some good information. So, to err on the side of caution, I should install a 9mm mainspring like this one http://www.gunpartscorp.com/Products/465390.htm Worst case scenario, it may not cycle .30 Luger ammo, but won't do any harm either. I always try to load to "Factory duplication" specs in my Lyman, FWIW.