I don't think your request is unreasonable, but generally speaking I wouldn't expect a gun store to give you all of your money back on your purchase towards a trade. In my experience you can expect to get roughly 60%. of course this will depend upon your relationship with the store.does this sound reasonable? I'm just looking for opinions
Now regarding you approach, if you are a loyal customer of this store, having purchased several guns from them and are having a problem with a purchase you should take it to them directly rather than asking for a refund through an email message. Being a loyal customer, you should know the name of your salesperson or even better, the manager and talk to them directly.