I don't think copperheads have the means to kill you outright by their venom. They will just make you sick and inconvenience you for awhile.
A big rattler, or big cottonmouth, is deadlier because of the length of it's fangs and the possibility of it delivering a larger dose of venom. The longer it's fangs the deeper it can inject the venom, and the more likely it is to hit a major artery or vein. It is entirely possible for a big rattler to kill you in a matter of minutes if it hits a major blood vessel. But, most of the time they don't, and they just make you mighty sick for awhile. An acquaintance died from a rattler bite, but it was really the heart attack that killed him, not the venom. He was a poster child for "Alcohol and rattlesnakes don't mix". Ever hear the phrase "Watch this!" ?
SRH
