As with all internet inquiries, online ecommerce sites use Keywords to browse their own website. And that's what it all comes down to, keywords.
When you want to find an item on Google, what is the first thing you do, type in a keyword. If you don't find what you're looking for, what’s the next thing you do? Change your Keyword!
Now imagine if you found the item you were looking for the first time, wouldn't your life just be that much simpler? If I have an item in the mind, and find it immediately, I am more likely to make a purchase that instant. If it takes me some time and I can't really find it.... you are loosing your 'impulse buy'.
Now, I know you think you may be using keywords when you type in a title or when you throw in an accurate description, but will EVERYONE looking for your item find it? Better yet, will everyone looking for a SIMILIAR item find your item? Because keywords can also create opportunities, not just exploit them.
As you are writing your description in your classified ad, remember that you are not writing for you, who already knows what the item is, you are writing for someone looking for your specific item, you are writing for someone looking for a similar item, you are writing for someone just browsing a general topic or you are writing for someone who isn't looking to buy, but can be persuaded.
As a previous post has said, I tell people to repeat themselves. Repeat yourself in as many different forms as you can think possible.
Beyond that though, you need to explain the use of the gun. Type in, "this rifle is great for plinking," or, "great for personal protection and concealed carry." The more keywords that are included in your description, the more your item will be seen.
If the gun has recently been featured in a movie, write that in the description, it can't hurt you, it can only help.