Reddit had a great post on this (Destiny)

by iconicbanana, C2-H5-OH + NAD, Portland, OR, Wednesday, January 14, 2015, 09:46 (3399 days ago) @ unoudid

Here: http://www.reddit.com/r/DestinyTheGame/comments/2n3y9h/iron_banner_weapons_and_what_to_roll_for_guide/

Specifically regarding Perun's fire:

Perun's Fire:
Red Dot ORS1/Hip Fire/Hammerforged/Any

The massive range bonuses of Hammerforged/ORS1 tighten the hip fire spread even further beyond the effects of Hip Fire and maximize the speed of the projectiles. Hip fire build to maximize OHKOs. I feel it's better to go for Range as the Vendor Light/BEWARE already has a flawless Stability build and Range has a nice effect on both the spread of the projectiles when hip firing and speeds them up to make it harder to strafe out of part of the blast.

Odds are 1 in 75 rolls.

Odds of getting any combination of Red Dot OAS/Red Dot ORS1, Hip Fire/Rangefinder and Hammer Forged/Perfect Balance are ~15%. Those are the best overall sights/perks, imo. I don't recommend Accelerated Coils on this gun as it barely alters the charge time. You're so close to the cap on charge speed that you don't get the full benefit; Light/BEWARE and other Fusion Rifles also hit max charge speed with Accelerated Coils but are higher in every other stat since their base charge speed is lower, making them better choices.