I got a new DO Final Rest II fusion rifle (I liked the 300 level version I had). so I rerolled this a few times and got Feeding Frenzy (kills speed up reload), Reinforced Barrel (extended range, slower reloads), Rangefinder (aiming down sights increases range). I was really happy with that roll as it gives me a sniper style fusion rifle. It really comes down to personal preference.

Don't ascend a gun if you intend to re-roll it for different perks. The re-roll will reset the damage level and the gun will need to be ascended again. So try for the perks you want first, and then ascend it.

Is there a good tutorial for re-rolling guns somewhere? I've never done it--didn't think to do it for Iron Banner, and I don't even know what perks to hope for.

It comes down to what perks you like, and how much you're willing to gamble on trying to get them.

It's a bit trickier than it was in Iron banner: there, you could buy two of the same weapon, roll one until the perks were okay, then roll the second until you had a better roll, switch back to rolling the first, etc.

I recommend looking up your weapon of choice on DestinyDB.com, and using that site to look at what perks each slot can hold. Once you've decided on a "perfect" roll, prioritize your chosen perks, and then start rolling. I usually pick two I really want, and try to get both of those.

For example, I really like fast reloads and higher ammo capacity on my handcannons, so I tried for perks that satisfy those needs- Outlaw and Extended-Mag/Field-scout worked well.

Question: why are you using Etheric light on brand new guns already? Shouldn't you be using it on older, non-reforgable firearms? Is Etheric light that common?

Also why guns? I'd think boosting your level would have a much bigger effect on what content you can do than ascending weapons right now. I was planning armor first, then weapons.

Don't ascend a gun if you intend to re-roll it for different perks. The re-roll will reset the damage level and the gun will need to be ascended again. So try for the perks you want first, and then ascend it.

Is there a good tutorial for re-rolling guns somewhere? I've never done it--didn't think to do it for Iron Banner, and I don't even know what perks to hope for.