Regardless of whether anyone likes this or not, people categorize things based on appearance. This is why I teach my kids that the way they dress is how they teach people to treat them. This is why I am dressed business casual in my office even though I have no appointments today. While I am not saying that this should dictate our choice of guns, we ignore this fact at our peril, and need to be prepared to address it.
Glenn's study is one of the things I discuss and cite when teaching about the legal issues of shooting and self-defense. Since that study, AR rifles have become much more common, but have also increasingly been the choice of mass shooters. Both factors will affect the jury's perception.
The Gary Fadden incident, discussed by Mas Ayoob in the March-April 2004 American Handgunner, is also worth considering. Gary used a full automatic rifle to defend himself in a clear case of self-defense. However, he had to spend much more time and money than would have otherwise been necessary because the prosecutor didn't like his use of a full auto rifle.
Lastly, years ago, Mesa, AZ police officer Philip Brailsford responded to a report of a man with a gun, which turned out to be a drunk individual showing an air rifle to a drunk guest in his hotel room, in front of the window. Brailsford was carrying his personally owned AR-15 type rifle. The rifle had “you’re f*****” printed inside the dust cover, becoming visible when the gun was fired. Although Brailsford was ultimately found not guilty, significant media attention was focused on the dust cover.
A video of the Brailsford shooting was posted on TPI. That video shows Brailsford very clearly acting like he is looking for an excuse to shoot someone. At the time of the shooting, the victim had followed Brailsford's instructions to get on his hands and knees and crawl towards him. The victim's pants were too loose, and the victim was shot while reaching towards them to pull them back up. No other officer perceived a threat at that point, and I would not have perceived a threat.
Considering all of the above, my suggestions are:
1. Act responsibly to avoid bad situations in the first place, and to stay within the laws of self-defense if a bad situation happens anyway. Avoiding going to stupid places, hanging out with stupid people, and doing stupid things mitigates the risk of being in a questionable situation. The principles of self defense are primarily what governs.
2. Consider how your choice of weapon will be perceived, and plan to deal with that perception. For example, “I selected an AR-15 type rifle because I knew that 5.56 mm. penetrates fewer walls than a 9mm, .45, or 12 gauge, posing less danger to innocent bystanders.” "I know that a miss endangers innocent people downrange, so I selected a weapon which helps ensure that I will not miss."
3. In my opinion, which appears to be supported by Glenn's posts above, the potential disadvantage in the appearance presented by an AR is not significant enough to avoid that choice in most circumstances, but cannot be dismissed entirely. However, NFA (class III) weapons, which are currently less commonly used, may hurt that perception more.
4. Remember that you are legally responsible for every bullet you fire, and a fully automatic weapon makes it more difficult to ensure that every bullet goes where it should.
5. Avoid skulls, monster or zombie decorations, vulgar or other potentially questionable slogans, or any decorations on a gun that could cause a bad perception of you or your actions.
I really like the idea proposed by Attorney James D. “Mitch” Vilos, who answered Glenn's question in the link above: file a motion in limine to address the issue of the gun's appearance in advance of trial. My best guess is that the motion will be denied but will cause the judge to be extra careful to prevent irrelevant, prejudicial material and statements from influencing the jury.