Yes and no. I have served on two juries. On one we had someone who did not understand that her opinion of the law was irrelevant and that she had top decide the case based on the law as it was written and not as she wanted it to be written. It took us two days to explain the way the law worked. We were getting ready to ask the judge for an alternate to be seated because she was not following the law. Hanging the jury based on a different perception of the facts is something different from hanging the jury because you do not like the way a law is written. I believe you will find it more than difficult to hang a jury because there is one person who does not like the law.
As for nullification, that would have to be a unanimous verdict and I think that is also unlikely to happen. Very many in this country believe that there needs to be regulations placed on the access to guns.
Not to fear. No one in this country seems to be willing to do anything substantive in regards to gun control. People will die each year. The left will say something needs to be done, the right will say nothing needs to be done and the stuff that is done will amount to nothing.
I just hope it never happens to me or those I know. The rest of you.... oh well.