Excellent start
It's a great first model, and I like your attention to detail. I rated 9/10 given that you are a beginner still: if VidGameDude had submitted this, it would have gotten a 5, but that's the learning curve for you. The 500 polygon limit is a stringent constraint in today's GHz world, but it IS useful for getting you to prioritize your polygons for maximum effect. With that in mind, your polygon priority is actually what I want to address.
By the looks of it, I'm estimating the following numbers of polygons: 100 on trigger+guard, 25 on barrel, 25 on the hammers, 100 on the decorative gold piece above the trigger, 150 on the wood butt, and probably 50 on random other elements. That's not well proportioned, given that the barrel is huge and dominates the model but the trigger and the decorative gold piece can hardly be seen. I would tone down the decorative piece to 10-20 polygons, the trigger and guard to 25, and then use the rest of the polygon limit to make the barrel more circular instead of octagonal. I mean, it doesn't make sense to have SO much detail on small pieces but to be so polygon-cheap on the second largest object in the whole model. Especially because later, you'll learn how to use textures to give some really fine detail to otherwise low-poly objects.
Hope this was constructive more than critical, and good luck on your class!