Regardless of the "federal law" if the state issues a medical card in your state you can use medicine and i have yet to see a patient go to jail because they bought medical marijuana while having a valid recommendation from a qualified physician.
If that was an enforced law by the feds all patients would be behind bars period!
As far as the weapons go, after all the recent shootings it is true that the Government is trying to disarm it's citizens as much as they can. MMJ shouldn't matter or at least it hasn't played a role for me to purchase or to own here in CA.