Hello,
For defense against cougars, which is better? 20g shockwave or .357 revolver?
If this is what you have either will work and while ammunition selection is important shot placement in ultimately the proof of adequacy.
Other considerations are equally important including:
Are cougars the top of the food chain in your area? If not, you might want to reconsider your choice.
How large are the cougars your encountering?
Terrain should also be considered. Is your predominant terrain open, heavily wooded, mountainess, etc. Cougars like to lie in wait from elevated positions in trees or rock ledges and pounce on prey attacking the back of the neck for an instant kill. Consider your time of response based on your terrain.
Are you working or hiking. If mainly hiking carrying a shockwave is easy; whereas, working with your hands you may be better off carrying a pistol. Also consider how you carry a pistol? Chest rig or holister on belt .
Just a couple of thoughts for your considration. I deal with black bears, cougars, bobcats and coyotes on a day to day basis. Based on the worst of my threats (bears) we carry both pistols and shotguns. 12 gauge shockwave loaded with OO buck and black magic slugs and a Glock 10mm with Underwood extreme penerator ammunition.
Bottom line is shot placement.
Regards