When my neighbor's lawn was assaulted by an armadillo, he came to me and asked if I could solve the problem with my air rifle. Two months later the opportunity presented itself and I dispatched the critter with a head shot at just under 20 yards. I used the .22 caliber H&N Baracuda Green, 12.65 grain with my TX200. When I shot the armadillo he kibitzed took a half dozen steps and fell dead. At that distance my TX200 was producing about 16 ft/lbs of energy. I'm sure that with a properly placed head shot a .177 could easily do the job.