Well I just finally got around to contacting them. Kept it pretty short and simple but backed up my reasons for supporting the 2nd Amendment.
Short and simple is the way to do it. When a congressional or legislative aide is going through emails, letters, etc they don't really take time to read them. They only care about two things:
1. Do you reside in the district their boss represents (in other words, are you a potential voter).
2. Are you for or against the issue.
If the answer to #1 is no, your opinion on #2 doesn't mean much. For #2, they just tick "for" or "against" for each piece of correspondence received, and give their boss the total.