I'd probably suggest working out what all the attachments are, including a breakdown of all that is available, and coming up with a price you feel is fair.
Forum sales etiquette/rules are that you do not solicit advice on a price before selling the item on here, as much for your own benefit (to avoid someone dishonestly lowballing you) as anything else.
It's very difficult to give you a fair offer based on a low quality photo that doesn't show all of the rifle, even more so when you haven't listed an estimate round count, date of purchase or a breakdown of what it is you actually have for sale.