Mission 50 – Kill the Butcher
Go to see Burke, and find out the Butcher's already on his way here to kill you all.
At least it won't be another car chase. You'll find yourself atop the shop, with a few sniper rifles nearby. Cars of enemies will peel into the lot- use a pistol to blow up explosive barrels, and take out survivors with the rifle.
The Burkes will call out targets for you, but it's hardly necessary. Goons who evade fire can climb the roof to get you, but they're easily punched, knifed, or shot as they clear the ladder- if you're paying attention.
A mini-cutscene will announce the Butcher himself, but all targets are pretty much alike to the Manitou rifle. The boss might soak up a few more rounds than his men, but take them all out regardless, then slide down the ladder.
You may want to take a meandering route to the Butcher, so you can scoop up dropped cash and ammo, but once you get close, the cutscene will complete the mission, and Burke's hold on Point Verdun.