This is an idea I've had for years, but I only worked out the details when I decided to post it just now.
For the purpose of training cyborgs or robots to dodge bullets, I propose live-fire training where the bullets have tethers, likely made of carbon nanotubes, to stop them at a predefined distance from the shooter.
Here is how it works:
Each bullet has a tether coming out of its rear end, and the tether comes out between the bullet and the casing. (There might be a small bulge or gap in the casing where it holds the bullet to accommodate the tether.) The rest of the tether is wound up on a reel. These are used with a special gun where the barrel is composed of two halves, sliced lengthwise. At one or both of the seams, there is a groove, straight along the barrel and deeper than those of the rifling. The barrel halves can be opened and closed by a lever on the receiver.
You load the ammo into the magazine as usual, stringing each tether out the front of the magazine opening, after mounting the reels onto a holder so the tethers don't get tangled. Then you put the magazine into the gun, with the barrel open, and run the tethers through the barrel. Next you close the barrel and seat the tethers in the grooves—maybe there's some adhesive or something to keep them in place.
At the firing range, you mount the reel holder to a fixture in front of you, and start firing (not before the RSO says so, of course). Each bullet strips its tether out of the barrel as it is fired, and the reel pays out more tether as it travels downrange. When it reaches the predetermined distance (marked by a line on the floor of the range), the tether runs out and the bullet stops.
"But won't the tether be ripped out of the bullet?" I hear you asking. That's not insurmountable. A steel frame in the core of the bullet should keep it from breaking up, the tether can go through the center of the bullet and be anchored to the frame closer to the front, and a brake on the reel should reduce the deceleration. Either activate the brake when the bullet is almost there (which it could fail to detect) or have a smaller secondary reel, which only holds enough tether for the last couple meters of the trajectory, with an always-on brake. That secondary reel could even be on the bullet itself. Once the primary reel is exhausted, the bullet starts drawing tether from the secondary reel, and being slowed down by the brake.-- notexactly, Nov 27 2015 These https://buy.taser.c...lections/cartridges [evilpenguin, Nov 30 2015] A gun barrel with a slice in it is a gun barrel that will leak lots of the hot gas that normally accelerates a bullet to its typical velocity.-- Vernon, Nov 27 2015 Wire-guided missiles unreel the wire from the rear of the projectile, not from the launch point, because of drag. A bullet towing a cable - however light - from a reel at the firing point is going to decelerate very quickly, and the ballistics will be woefully unpredictable.
Since the bullet is also spinning due to the rifling, how is the tether prevented from tangling ?-- 8th of 7, Nov 27 2015 //the purpose of training cyborgs or robots to dodge bullets//
I do not approve of this aim.
I think you'll find the tether to be impossible to design. Magical carbon nanotubes won't make it any more practical. Instead, why not just use a whiffle ball style projectile that slows down rapidly after being fired?-- Custardguts, Nov 29 2015 Because the ballistics are dire. For accuracy, high velocity is required.
The primary force acting to decelerate a projectile in flight is air resistance (proportional to frontal area and drag coefficient, square-law to velocity).
Heavy projectile good, lightweight projectile bad.
Rifle rounds can be lethal up to five miles, but are only accurate (with a few exceptions) out to about 800 m.-- 8th of 7, Nov 29 2015 //high velocity is required// - yeah, but the stated aim here is for a training round, right?
I'm down with ballistics, in fact I spend quite a bit of my spare time using my engineering/physics knowledge experimenting on finding the optimal terminal ballistics package for terminating, as it were, various feral animals that reside in my area. As my past posts would probably show. Right now the best in class is a .30" 130gr barnes hollowpoint copper projectile doing around ~3200 fps, which is about the closest thing to a grenade I've seen, outclassing much larger and more powerful rounds produced from other firearms. But I digest.
Op wanted to get a bullet to stop on a tether. I don't think that's possible. A whiffle projectile is one way to do this, if you keep the range within certain limits. Second option is to use a compounded projectile (I think bismuth is used) with a small explosive charge that detonates a fixed (or variable) time after firing. So the projectile construction is dense metallic powder pressed into a shape, which when the small explosive charge detonates, comes apart into a cloud of dust which very rapidly decelerates and settles out.
Problems would be a) how big and ballistically viable the electronics and detonator are, and if they are still a hazard, and b) how reliable said electronics are.
I still don't agree with training borg to dodge bullets.-- Custardguts, Nov 29 2015 use a giant lazer-- sninctown, Nov 30 2015 Carbon burns. The fact it's in nanotube form doesn't change that. In fact, any tether that you can fit a coil of behind a bullet will burn. Putting it between bullet and the shell casing means it's in with the propellant. Meaning it burns.-- MechE, Nov 30 2015 Hey bro. Hot tip. Robots can be made of materials that are "bullet resistant" even to the point of being bullet "proof".-- WcW, Nov 30 2015 // A gun barrel with a slice in it is a gun barrel that will leak lots of the hot gas that normally accelerates a bullet to its typical velocity. //
It clamps together. It can be machined so that the mating surfaces mate very precisely. A gasket made of lead could be used if necessary.
// A bullet towing a cable - however light - from a reel at the firing point is going to decelerate very quickly, and the ballistics will be woefully unpredictable.
Since the bullet is also spinning due to the rifling, how is the tether prevented from tangling ? //
These problems have a common solution. The reel doesn't rotate like a winch to pay out tether; it has one open end facing downrange and the tether just unspools. Normally this would result in the tether twisting, but the bullet is spinning.
I admit that this complicates braking if you want to use the same reel for braking. But a separate reel for braking purposes could be winch-style. Or the brake could be implemented as rollers that are clamped onto the tether, between two open- ended reels.
// Carbon burns. The fact it's in nanotube form doesn't change that. In fact, any tether that you can fit a coil of behind a bullet will burn. Putting it between bullet and the shell casing means it's in with the propellant. Meaning it burns. //
Good point. I can't believe I missed that.
Let's put some kind of ablative coating on the part of the tether exposed to fire. Maybe the stuff they use for atmospheric entry.
Or just use an airgun.-- notexactly, Nov 30 2015 random, halfbakery