"Original statement is extremely vauge"
This doesn't challenge whether the statement is true, it challenges whether the statement is useful. If you think it could be made to be more useful you can use the "suggest edits" feature, or write a new statement. (It might be worth considering that if you successfully argue that a statement is too vague you haven't actually defended any position about gun laws.) It would also make sense to say what is too vague about it.
It is NOT the case that "New gun laws will reduce mass shootings in ways other than preventing shooters from obtaining guns."
The statement above does not appear in any challenges, supports, or specifications of other statements.