Up to 5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
7.5-15% Weak Spot Damage. Weakspot Kills also ignore Enemy Hit Mass.
5-8% Strength for every 10% of magazine spent during continuous fire. Stacks 5 times.
2-5 bullets loaded from Reserve on Critical Hit.
I've slaughtered Daemonhosts, Plague Ogryns, and Beasts of Burgle with this build. Try and aim for their weakspot for maximum efficiency.