Prepare to eat a lot of beans.
The best strategy I have ever seen for wannabe retail gun dealers is accessories. Push the accessories. Sell the gun at enough margin to cover your costs, but never let a deal close without a "package". The package might be any combination of things like a case, sling, holster, spare mags, ammo, ear protection, eye protection, etc. If you just try to sell guns alone, you will fail. There are big gun retailers that have razor thin margins and they make up on margin.