If it's currently on a Form 4: you need to Form 4 it to an FFL/SOT in the buyer's state;, then he Form 4's it from them to him. Yes, two stamps.
Alternatively, if the seller is a resident of your state, I believe you can still Form 4 it directly to him. However, I am not sure how this works now with the 41F changes, trusts, and the eFile changes. It used to be you'd just both sign the paper form and send it off. This is one stamp.