I could have sworn we’d handled this one. But, I can’t find it. Anyway, chain by itself will make for a fairly effective improvised whip. Adding a padlock, or any other solid weight to one end would turn it into a kind if improvised flail. In both cases, you’re talking about weapons that can do a fair amount of damage.
With chains there’s enough size variation that you could end up with links too light to do anything meaningful. If it’s a chain that was used to lock a gate, or even just a bike, then it should be heavy enough to inflict some nasty injuries, even without the lock.
Without a weight, I’m not sure if arm length is long enough to really build momentum easily. But, when you add a padlock, and that stops being an issue. The weight (it doesn’t have to be a padlock) turns the weapon into a kind of flail. At that point the flexible portion (chain in your case, but you could just as easily use electrical cable, nylon rope, or any other flexible material on hand) is only there to generate momentum, which you deliver via the weight. Arm length should be enough to seriously injure or kill.
Again, it’s possible you’d end up with a padlock too small to do anything serious, but a medium lock, and even some bike locks, will be large enough to wreck someone, once you get them moving fast enough. As with the chains, there’s a lot of variety, but any lock
intended for commercial or industrial use should be solid enough to work
Most padlocks can easily take more abuse than you’d be inflicting from using it as a flail, so that’s not a problem. These were designed to take a few kicks from an angry bystander, or being backed over by a truck, so connecting with someone’s skull isn’t going to be much more strenuous.
As far as I know, there isn’t much sophisticated about using these things.
If it’s long enough, you hold it with both hands, about shoulder’s width apart, and generate momentum with the leading hand. Most quick strikes are dealt that way, but you can release the leading hand, or adjust the grip on the fly to extend the reach.
The distance between the weight and the leading hand will directly control how fast it generates momentum. It’s easier to get it moving, then ease your leading hand back down before striking, than generating momentum using the full length of chain.
Your primary goal is to strike with the weight, rather than with the flexible portion. If you fail that, the weight will wrap around anything you connect with, as its reach allows. Tangling it around your foe’s neck or weapon isn’t a problem, but tangling it around a steam pipe or clothesline is a big one.
If it’s not long enough for a two handed grip (arm’s length wouldn’t be), you hold it with one hand. (Possibly running it across the palm, over the back of the hand, and through the palm again to aid with grip.) You then generate momentum with that wrist, since your off hand doesn’t do much at all. Because you’ve only got one hand on the weapon, you can’t regulate it’s momentum or reach, and need to account for those with every swing. It’s also slightly harder to protect it against being tangled, as a result.