The only weapons that don’t malfunction are rocks and maybe some one piece edged / pointed implements. Anything else should be carried with the expectation of remedial action being a possibility during employment, there are too many factors with firearms (ammo, environmental, positional, etc...) to think all of them will work in all situations. Know the limitations of your tool and carry on. That being said a firearm that isn’t “reliable” should be shit canned, what level of “reliability” is “acceptable” in a “working capacity” could be argued but there are some fairly well documented testing protocols out there that I’m comfortable with using as a guide to determine that.