Up to 5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
3.5-5% Strength for 3.5s on Hit. Stacks 5 times.
5-8% Strength every 0.4 seconds while aiming, stacking 5 times. Discharges all stacks upon firing.
Hitting at least 3 enemies with your secondary attack grants 15-30% bonus to Strength on melee attacks for 3.5 seconds.