You say “sufficient“ which makes me think you’re referring to lost muzzle velocity compared to a 2” or 24” barrel... if so, don’t. It’s negligible and completely irrelevant if you’re talking about killing animals. What is more important is the added muzzle blast. Any single rifle shot without ear pro (even if you’re “in the moment“ and “don’t hear it”) does permanent, Irreparable damage to your hearing. In short, without ear pro, the 20” will be less pleasant than a 22” or 24” tube, but all of the above will kill the same and damage hearing as per standard. You do gain handiness going short though, which outweighs minuscule losses in velocity when talking tubes of said length.