Not saying they do/will. Just saying that it's hardly surprising that jurors chosen from among the typical Motoring Public (old reference) may bring their conscious or subconscious bias with them to the jury box, and America's Rifle (AR) may, or may not, be something that in their minds has been shown to be good, bad or indifferent. The same might be said for a bolt gun, or a lever gun, or a 12GA used for birding, skeet or clays, compared to one tricked out for a Zombie Apocalypse. Naturally, the area of the country in which a jury might be chosen may have different factors at work in this regard.
Like with everything else in life, the freedom of choice doesn't mean a free pass from having to choose wisely for any particular circumstance that may come along. Also, good attorneys can do good things, but if they're required to put in extra billable hours to try and deal with the consequences of 'predictable is preventable' decisions made by their client, don't be surprised if it takes more work, and more money ... and there's no guarantee they may change the minds of someone who sees black rifles as evil, or indicating something about the mindset of someone. People. It's what they do.