Up to 5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
Hitting an enemy gives them 1-4 stacks of 2.5% Brittleness. Debuff lasts for 5 seconds and can have a maximum of 16 stacks.
5-8% Strength for every 10% of magazine spent during continuous fire. Stacks 5 times.
7-10% Movement Speed Reduction for every 5% of magazine spent during continuous fire. Stacks 5 times.
I make it a personal quest to shoot at least 5,000 stubber rounds a match and so can you. (Ripper Gungryns have a good day shooting at least 1,000 ripper rounds.) Unlocked and Loaded consolidated Gungryn blasting on the active ability so you can pick freely between rending rounds (good for the heavy stubbers) or flame bullets (good for Foe-Rend Mk V Ripper Gun and the Achlys Mk VII Twin-Linked Heavy Stubber) as your heart desires. My Ogryn is patterned after hero of Terra, Zangief, and so the original pick, the Borovian Mk III Delver's Pickaxe with Wrath and Slaughterer , provides a solid compromise between spinning wild heavies and pulling in folks to bonk carapace. Post-Grim Protocols, I like the Branx Mk Ia Delver's Pickaxe for single target piledriving and toughness regeneration when the gun isn't firing. These days after the Mortis Trials update, the newly buffed "Brunt Special" Mk I Bully Club with Thunderous does a great job debuffing for the team and doing solo melee clear while the bulk of the build revolves around gunnery.
The team still appreciates Soften Them Up, the Frag Bomb, and a truly absurd amount of suppression. Single target heavy melee hits and both 25 toughness nodes let you stay up and running in hairy melee situations. Bigger coherency aura is just responsible team play. I like the Krourk Mk V Twin-Linked Heavy Stubber for a balance between Flak armor breakpoints and ammo efficiency, and since Nightmares and Visions introduced Concentrate the Gorgonum Mk IV Twin-Linked Heavy Stubber is rock solid. When running the Gorgonum Mk IV Twin-Linked Heavy Stubber it gets a bit ammo hungry so maybe expect 3,500 rounds in a full match; Achlys Mk VII Twin-Linked Heavy Stubber can pretty reliably hit 6,000 rounds fired. Brute-Brainer Mk XIX Latrine Shovel, the Krourk Mk IV Cleaver , and the "Brunt's Pride" Mk II Bully Club all function great as backup melees. This tree also works great with the new single barreled Heavy Stubbers - the Krourk Mk IIa Heavy Stubber 40-rounder with Blaze Away and Overwhelming Fire, the Gorgonum Mk IIIa Heavy Stubber 30-rounder with Opening Salvo and Pinning Fire, and the Achlys Mk II Heavy Stubber with Headhunter and Opening Salvo. Ability recharge goes faster when you keep blasting so don't be shy about shooting folks when ability isn't up.
Do play the Street Fighter 2 soundtrack while you play Darktide, it's great for morale.