However, if you do this 30 times a year, and make income from it, that is something else entirely.
OP, presumably you will sell the gun at cost or at a loss. It seems that the only possible source of information to be used against you would be the buyer. Who else could accuse you? So it might be worth getting written proof of the sale price from the buyer. That way no one accuse you of intending to engage in illegal trading.