Up to +5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
+5-8% Strength for 4.5s on Kill. Stacks 5 times.
+5-8% Strength for every 10% of magazine spent during continuous fire. Stacks 5 times.
Up to +2-5% Strength, scaling with remaining Ammunition. Stacks 5 times.