Can you really knock someone out quickly with a blackjack/slapper, or are they pretty much used to just beat someone to death?  
I'm curious if there really is a technique to swing one of these and knock someone out, and if so how do you do it?  I'm assuming if this were the case, any blunt weapon would do.

If you knock someone out you're fairly close to killing them. I think most people would be better off with a folding knife or pepper spray. The knife gives you more lethal and non-lethal options than just a whack to the head and is better in grappling situations, and the pepper spray is non-lethal.

One of our oldtimers used to carry one, and still swears by it, although he can't use it anymore.

His technique was a quick "slap" to the sides, top or back of the head . It usually resulted in an unconscious or semi-conscious, compliant adversary.

These saps can apparently cause pretty severe brain damage or death, however, and a blow to the head with one would be considered deadly force in most places. I think my coworker just got lucky that he never seriously injured or killed anyone.

Ive seen a blackjack used by delivering blows to the back of the knee/upper thigh with great effectiveness. Took the person down almost immediately and when he got up it wasn't very fast.

Hitting somebody really hard with a metal bar is going to make them quit what they are doing or at least think about it for a second no matter where you hit them. It would probably be pretty easy to break some ribs for that matter.

Michael

For many years I carried a blackjack. It was the kind with the spring in the handle. Other guys carried the flat "sap" style.
I have never been able to knock someone out with one, but I was also trying not to kill them. You can stun people with them, but every time you hit them it opens a cut on their head and you are going to have a bloody mess.
If you really hit someone as hard as you can with one you may kill them. However, I have seen a man take 100 stitches in his head and never loose consciousness.
In the new age the best deal IMHO is the pepper spray/asp baton combo. When it's time, spray them and shove them backwards. Give the spray a second or two to start working. Then reach out with your left hand and grab his shirt at the left shoulder. At that time start whipping his legs with the ASP.
This is what I call the "standard attack" and it works great. If he turns toward you to hit you, just go with it and you will be behind him enough he can't hit you.
 Just keep hitting his legs and don't let go of his shoulder and he will fall down. The only time it's not good is when he doesn't have on a shirt or rips out of his shirt right off.
Just remember to use plenty of force early and that will help alot. Believe me it is easier to maintain control than try to regain control.
I would stay away from the blackjack. The standard attack puts them down but doesn't really injure them unlike the blackjack. I would also recommend running 3 miles every other day and lifting 2 days heavy/2 days light every week. Most people can only fight about 45 seconds. Make sure you can fight longer.

Was the consciousness too tight?

You can certainly knock someone out with a single blow. Just make sure you hit them is the head. Preferbly the front or back as there is a lesser chance of a skull fracture on the stronger rounded parts (front/back) of the skull then on the flat sides. Statistically, lasting head injuries are more prevalent in trauma to the sides of the head than to the frontal and occipital regions. You could also break a clavicle, or crush fingers or fracture an orbit or two(bones around the eyes) with repeated application of a slapper. It is a viscious weapon when used. Have no allusions when it's in your hand. If you plan on striking someone with it you have absolutely entered the realm of Deadly Physical Force.

It is designed to inflict crushing injuries wherever it lands. Check your local laws about possesion and whatnot. Here in NY when a LEO uses a slapper(a slab o'lead in a nice leather case) it's considered deadly physical force. You'll need to be able to clearly articulate how and why the usage of the slapper came into the fray. It is a device designed to inflict serious physical injury when correctly applied to the right body parts, and is by no means equatable to chemical munitions(Mace or pepper spray) so be careful.

I believe here in NY they're illegal except for LEOs.

Sherm

Sherm, same as being caught with a switch blade, Brass Knuckles, or even the first violation of possession a unregistered gun.  Class A Misdemeanor

Go to the book store and get one of those leather weighted tools used to hold a book open...pat

I have to agree with mcgredo...It would also be a bad thing to defend in court(as these things always end up in court)...I have used a quick blow to the throat area and this stopped the guy in his tracks ,I do however understand the possibility of crushing someones throat this way.  I still belive this would be easier to defend in court than a stick of wrapped up lead...Crazy how every decision comes down to how the courtroom is gonna view it...

Okay, this is for info only, so you people don't go playing games. Do NOT do this to yourself. You can injure yourself this way or someone else, if you try it. So please don't?

I'm gonna tell you how you can drop someone, or at least stun them, with one blow, using a blackjack, or the edge of your hand. You can also paralyze/injure/kill them. So don't play. You don't point guns at people, so don't go beating them with a blackjack or sap to test this.

Now i'll stop being daddy.

Feel around the back of your head. Right where the two lower lobes of your skull sit, right at the nape of your neck. Feel that indentation? Top of your spine. Go a fingerwidth or two below that, and this is your intended area. Lots of nerves here. Good, swift strike from the edge of the hand or a blackjack to this area will stun someone. If not knock them out.

For you people that will be inattentive and try doing this to yourself, or someone else, make sure you strike lightly. A soft blow is all it takes to see that this area DOES produce an effect. You'll feel a good tingle in your neck and a moment of faint disorientation.

Anyway. Please remember that this is not a game, and is to be used only in a deadly force situation. Otherwise, leave well enough alone and don't go looking for 'magic spots' to hit people.

Mattimeo, I'm just waking up(2 hours later) after trying out your method....IT DOES WORK!!!