Your REAL problem with nicotine is the stuff they sell it mixed with; That tobacco will KILL you. Too bad the FDA won't let the nicotine companies sell their product unless it's mixed with a very poisonous plant... I shudder when I think how many lives that government policy has cost!
My understanding of the medical effects of both these stimulants is thus: (Keep in mind I took my last physiology course about 15 years ago!) The body will adapt to a moderate input of just about any stimulant. If you drink caffine regularly, or smoke, the only way they're likely to effect your performance is if you either take an unusually large dose, or stop taking them, immediately before the effort. This puts your body into a condition it's not adapted to. For some athletic events requiring fast reflexes and maximum exertion, but NOT a lot of fine motor control, caffeine has been shown to improve performance marginally, but only if you're not habituated to it. Marksmanship is obviously NOT one of these events!
Now, I said "moderate". Don't know about nicotine, but caffeine causes neurotransmitters to be released in your brain, but does NOTHING to promote their replacement. Over-use of this stimulant eventually exausts your neurotransmitter stores, at which point caffiene ceases to be an effective stimulant, and it becomes VERY difficult to think, or do anything else requiring a nervous system, until you've had an opportunity to rebuild them. Which can take from hours to days, depending on a number of factors.
There ARE "smart drinks" available mail order and at health food stores, which combine caffiene with nutrients which are precursors to the effected neurotransmitters, so that you don't suffer this effect. Sadly, these nutrients, like choline, taste REALLY bad, so nobody is going to chug these beverages down for the taste. You might think of them as over the counter uppers with minimal side effects.
Now, interestingly, there is a drug, used for treating narcolepsy, which will keep a normal person awake and alert for DAYS at a time, with no apparent side effects. Naturally, it's strictly controlled.
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Sic semper tyranus!