[b]Step 1: Figure out what's available.[/b] Use a database like [url=http://db.planetdestiny.com/items]PlanetDestiny[/url] or [url=http://www.destinydb.com/items#type:1498876634]DestinyDB[/url]. Search for the weapon you're planning to reroll, and figure out what perks are possible. [i]Do this before you start rerolling[/i]. You don't want to find out you wasted 50 motes trying to get a full-auto pulse rifle or a hand cannon with Firefly. Edits 1-2: You can reforge Iron Banner guns at the Gunsmith, even though they don't have the Reforge Ready perk. (Hat tip to Altros for the reminder.) As reported by several others below, and confirmed by my own experiment with my Gheleon's Demise, these still use their [i]pre-HoW[/i] loot tables. [b]Step 2: Create an achievable plan.[/b] If you go in saying "I want a scout rifle with Full Auto, Explosive Rounds, and Zen Moment," you're going to end up poor and disappointed. The median number of times you need to reroll to get just Full Auto is 6: half the time it'll be more and half the time it'll be less. The median number of times you need to reroll to get Full Auto [i]and[/i] Explosive Rounds is 22, which will take a while to get but is still achievable. But the median number of rolls to get Full Auto, Explosive Rounds, [i]and[/i] Zen Moment is 178. That would be a great gun, but you're going to go broke trying to get it. So instead of going in with an exact picture of what you want, pick [b]just one[/b] perk you can't live without, and then maybe two or three you'd like to see elsewhere on the gun. So maybe instead of that very particular Full Auto/Explosive Rounds/Zen Moment roll, you want Full Auto and a talent that increases stability (Smallbore, Braced Frame, or Hand-Laid Stock). That's a median of 13 reforges to pick up, which is completely feasible. [b]Step 3: Know when to quit.[/b] Once you get to your planned version of the gun, resist the temptation to try for a better roll. That's the equivalent of adding extra requirements in Step 2, and it probably pushes you back to that place where you'll be rolling 180 times. Get to the version of the gun you decided to get in Step 2, then [i]stop rolling[/i].