I've only used cans on hunting guns in South Africa since there is no legal way to possess one in my state if you're not a manufacturer or government agency.
CMG Recoil Reaper can (not sure if available in the USA) on a hunting weight Howa 1500 in .338WM (about 9lbs with optic) running 250gn pills at full steam I was able to see impact sign on an eland at 300m but was not able to observe bullet trace due to recoil. I was only able to see it's side ripple slightly before it jumped. Relatively low recoil remained but still, it's a big bullet going pretty fast. The shot was fully proned out with good load on the bipod. I couldn't deal with the recoil of that thing unsuppressed. I'm a sissy that way.
Similarly, .300WSM with 180's running fast, Tikka T3 action, carbon fibre barrel, GRS chassis, US Optics scope + unknown brand suppressor. I saw the head of an impala detonate at about 75m and then was looking more or less at sky. That shot was taken from bags on a padded rack on a land cruiser. I was, however, able to watch the bullet trace as a 180gn .30 cal pill sailed just over the back of another impala at 300m (lesson: check your turret settings before shooting). That shot was taken proned out against a 2' tall berm with bags supporting the front end and my fist for rear support. The gun was reportedly unshootably hard kicking without the can on it. I never tried shooting it unsuppressed because, as stated, I'm a sissy about recoil.
In any event, all of those shots were greatly aided in terms of shot spotting from behind the gun by the presence of a can but my position, a natural point of aim and the distance to the target were equally major factors in being able to spot trace and impact.