AFTER SPENDING CONSIDERABLE TIME COMPOSING THIS MESSAGE, i DISCOVERED THAT IT WOULD NOT SEND, APPARENTLY BECAUSE THE IDIOTIC SPELL CHECK FEATURE DIDN'T RECOGNIZE MANY OF THE WORDS AND DRUGS I'D WRITTEN. HAVE DELETED THESE, SO MESSAGE WON'T MAKE MUCH SENSE IN SOME AREAS, AND WON'T CONTAIN THE NAMES OF THE DRUGS I LISTED. MOST OF THESE CAN BE FOUND ON - IMBECILIC SPELL CHECK DOESN'T RECOGNIZE THIS WEBSITE NAME, EITHER - GO TO THE PREMIER ENCYCLOPEDIA WEBSITE; NAME BEGINS WITH WI.
Can't believe a few of the previous answers - nitwits watching too much TV (although there are more than a few grains of truth in several of the responses). Reality is that there is NO semi-auto dart gun, tranquilizer (actually usually anesthetic) or otherwise, for a variety of reasons, which I'm not going to go into. As an anesthesiologist (and former sniper - 'Nam) who has anesthetized many hundreds of animals over nearly 30 years (volunteer work), the dart guns range from the blow guns that we use in zoos on small to medium-sized animals in holding cages to expensive-to-incredibly-expensive air- or CO2-powered rifles (& pistols) for outdoor game, to dart guns powered by .22 cal. blanks. The latter are the most 'powerful' and have the longest effective ranges (important when dealing with dangerous game) but are handicapped by only accepting small, low-capacity darts for longer ranges, thus necessitating use of extremely potent narcotics, which one would like to avoid unless necessary, which it almost always is. Once upon a time, there used to exist a dart gun 'fired' by a rifle blank, firing a dart that (after removing safety device before loading), when striking target, detonated a tiny explosive charge to inject contents. Was only for the thickest-skinned, most dangerous game. I dropped an elephant @ ~175 yards. once with this rig - was an emergency and never would have attempted that range otherwise (elephant did fine after treatment). This gun (semi-custom) and its darts are long gone, although there is a company in South Africa that claims its CO2-powered dart rifles have a maximum range of 130 meters - I can't comment on this. The blowguns are for zoos or small, slow animals only, have an effective range of a few feet, and are only for experienced users. Advantages are lack of bruising, ability to use K drug in 5-10 cc darts (again, only for small-medium animals), inexpensive. The dart guns with the longest range are the ones powered by .22 cal. blanks, with size of darts varying from 1cc to 5cc, but big limitation is size of dart. 1 cc. supposedly accurate to ~100 yards. Rubbish. I've never placed a shot w/ 1 cc. dart beyond ~80 yards. accurately and consistently, and that under ideal conditions (no wind, stationary or near-stationary target, etc.). For longer ranges with the .22 blank guns, dart size eliminates every agent except super-narcotics, unless one were trying to hit a small animal (remember, animals differ in sensitivity to all agents used, practically speaking) with K drug or a tranquilizer, or some other animal with some agent (vaccine, etc.) that could be contained in small dart. The air- and CO2-powered dart guns are expensive (some costing as much as a superb sniper rifle - $5000.00) and, depending on the size of the dart, aren't reliable beyond 40-60 yards, usually considerably less. I have a variety of dart guns, rifle and pistol, and when I'm faced with nailing a dangerous critter, I ALWAYS use a special blank-firing gun I have, from as far away as possible, from a vehicle or chopper if possible [or even in a cage - just turn down the power feature on the gun], and with my .500 NAME caliber (has a gunsmith's name attached, which the imbecilic Spell Check feature doesn't recognize (an extremely powerful .50 cal. revolver - not quite as powerful as the .500 S&W Magnum, but the pistol isn't 2 feet long and doesn't weigh 6 lbs., either) in a belt holster - the latter just in case (even, in a shoulder rig, in zoos, etc. - don't tell anyone. I'd probably commit suicide if I had to kill a rhino, elephant, etc., but there are almost always others about who risk injury).
Now to questions: 1) How fast does 'tranquilizer' dart work? Very complicated. NOT LIKE ON TV!!!! Depends on drug used, where it was injected (fat v. muscle v. [in gut - always a mistake hit] v. subcutaneous v. etc., how much was injected, animal sensitivity (this gets into pharmacology subjects that could fill a textbook), and other factors. Let's use the hypothetical healthy Alaskan brown bear (grizzly) @ 700 kg. - the only drugs anyone in their right mind would use outside of a zoo [and inside it, too] would be C drug or E drug, preferably the former (more potent narcotics exist, but are expensive, rarely available). Assume a heavy dose, a perfect hit in rear hindquarter - everything perfect. I've seen grizzlies in just such a setting take 45 min. and longer to go down - still not out, still fighting mad and slashing about. When they appear to be 'out', will often surprise you, and nothing surprises like 1500 pounds of FAST, angry grizzly, even sedated. When they are 'out', I always try to intubate, but what appears to be an anesthetic dose of C drug often isn't when you go sticking a big tube down his/her trachea. What to do then? Give more C drug and risk not being able to intubate/ventilate the bear, and /or risk that the antidote you give to wake bear up will wear off before the C drug does, or will be insufficient dose w/ drowsy-but-fighting bear preventing you from administering more antidote W/O re-darting bear, and bear dies? Enough. Typically, given everything perfect, brown bear w/ average dose of C drug starts to stagger after 15-20 min., and can be 'out' after 30, but always varies. 5 seconds - forget it. No insult, but TV land nonsense.
2) When dealing in any way with a brown bear, one wants them OUT, as close to unconscious as possible. Problem is, gotta get the drug in a small-capacity dart (even if it's 10 cc). PCP could be concentrated enough to be considered, but FDA outlawed its use for humans in 1965 and for vet usage in 1978. K drug, which is a fine anesthetic for smaller animals (and humans), cannot be concentrated enough to deliver an anesthetizing dose to a large animal in a dart. A-drug is routinely used to tranquilize a variety of animals, but a tranquilized grizzly is still a conscious grizzly. Forget it, not to mention the fact that in current form, one would have to inject a 700 kg. grizzly with ~150 cc of drug. If the bear wasn't angry before, squirting that much solution intramuscularly, etc., would change that! Are other bizarre, dangerous options, but the only reasonable ones to use are C drug, a synthetic opioid of extreme potency (10,000-100,000 times more potent than morphine), and E drug, another synthetic opioid (1000-3000 times more potent than morphine). Neither are ever used in humans - every few years, one can read about some moron(s) breaking into a large-animal vet hospital, stealing the C drug (which sounds like F drug, commonly used in humans), and inevitably spilling some on their skin, where it is rapidly absorbed and leads to respiratory inhibition and death.
If you're worried about encountering brown bears, use common sense. Make plenty of noise so they'll hear you coming, pay close attention ALWAYS to your surroundings, and if you do run into one, stay calm, back away slowly, and fire your handgun/rifle into the ground or air (if you're not carrying one of these, have one of the SERIOUS gas-powered portable air horns [good ones are bigger than my .50 caliber handgun, and should emit 140-160 decibels of noise - deafening] with you at all times in bear country. This only applies to areas with polar bears [won't be any left in the wild in 10-20 years, thanks to us], or brown bears (incl. grizzlies). Black bears are simply not as unpredictable, although I don't recommend approaching them - back away.