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Military technology: Magic bullets

economist.com

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Re: Military technology: Magic bullets

#31

Post by regularfry »

jgrahamc wrote: post #30

My stab at how the bullet measures its own rotation: Suppose the bullet leaves the muzzle rotating at 300,000 RPM (quite reasonable for a rifle). That is 5kHz. It's easily within the capabilities of a Hall Effect sensor to measure a 5kHz rotation and so I'd make the very centre of the bullet contain a free rotating magnet. The rifle itself sets the magnet spinning at some known rate opposite to the rifling. When the…

I suspect it would be easier to make the front spin and fin-stabilise the rear than try to make a rotating core. That being said, given a known muzzle velocity I don't understand why it's not a simple timing problem.

Re: Military technology: Magic bullets

#32

Post by sbierwagen »

regularfry wrote: post #31
jgrahamc wrote: post #30

My stab at how the bullet measures its own rotation: Suppose the bullet leaves the muzzle rotating at 300,000 RPM (quite reasonable for a rifle). That is 5kHz. It's easily within the capabilities of a Hall Effect sensor to measure a 5kHz rotation and so I'd make the very centre of the bullet contain a free rotating magnet. The rifle itself sets the magnet spinning at some known rate opposite to the rifling. When the…

I suspect it would be easier to make the front spin and fin-stabilise the rear than try to make a rotating core. That being said, given a known muzzle velocity I don't understand why it's not a simple timing problem.

Muzzle velocity varies quite a lot based on ambient temperature, air pressure, altitude, and propellant grain size.

Re: Military technology: Magic bullets

#33

Post by grannyg00se »

icegreentea wrote: post #23
dimitar wrote: post #3

$25 bullets and $25000 rifles are insanely expensive. And I don't see how better rifles will bring an advantage - most coalition casualties are from mortar fire and improvised explosive traps - rebels have already lost preference for gun standoffs. But I'm sure H&K and Alliant will love to sell lots of these to whatever army is corrupt enough to buy them. Also... aren't exploding bullets illegal under the Hague conve…

The Hague forbids bullets that expand on penetration, on the basis that it creates larger and more traumatic wounds. This round acts more like a grenade. It explodes (and wounds/kill by shrapnel) near the target. It shouldn't actually hit the person. Completely different class of weapon. It's more accurate to call this a grenade launcher than a rifle.

It always seems so absurd to me that there are rules around wartime killing. Once you acknowledge that it is acceptable to take another person's life for profit you really have little credibility for laying out rules of fairness.

Re: Military technology: Magic bullets

#34

Post by jmmcd »

sbierwagen wrote: post #16

Ah, the XM25. Last publicity blitz we saw on this was a year ago, and Gary Breacher called them out on it: http://exiledonline.com/xm25-gee-whiz-how-can-we-be-losing-w... (Even the file photo is the same!) The XM25 autocannon is neat. Absolutely nobody denies this. It's also pretty useless, because any insurgent who engages security forces in a conventional gun battle is going to die. Nine times out of ten, they're d…

The article was disappointingly flag-waving and uncritical.

Re: Military technology: Magic bullets

#35

Post by anamax »

__alexs wrote: post #7
ck2 wrote: post #6

Earlier quoted context omitted.

There are lots of "end-runs" around the Hague http://en.wikipedia.org/wiki/Expanding_bullet#Law and note that domestically governments do not have to obey even the most basic "rules of war" when they set police against their own people

Does Afghanistan even get covered by that stuff since no formal declaration of war has been made according to Hague Convention III?

Does it matter whether both parties are signatories?

Re: Military technology: Magic bullets

#36

Post by awakeasleep »

antihero wrote: post #18

Ah, humanity, always figuring out better ways to murder other humans.

Yep. It'll be great for this company once the regulations are loosened and they can begin selling to all the countries onnafrica, the middle east, western Europe, and Asia. Bad for everyone else though.

Re: Military technology: Magic bullets

#37

Post by mhb »

jgrahamc wrote: post #30

My stab at how the bullet measures its own rotation: Suppose the bullet leaves the muzzle rotating at 300,000 RPM (quite reasonable for a rifle). That is 5kHz. It's easily within the capabilities of a Hall Effect sensor to measure a 5kHz rotation and so I'd make the very centre of the bullet contain a free rotating magnet. The rifle itself sets the magnet spinning at some known rate opposite to the rifling. When the…

Ten years ago, I had a $2 top with LED lights which cleverly displayed words in a fixed position by using a sensor to use the earth's magnetic field as a reference.

Re: Military technology: Magic bullets

#38

Post by jcurbo »

__alexs wrote: post #7
ck2 wrote: post #6

Earlier quoted context omitted.

There are lots of "end-runs" around the Hague http://en.wikipedia.org/wiki/Expanding_bullet#Law and note that domestically governments do not have to obey even the most basic "rules of war" when they set police against their own people

Does Afghanistan even get covered by that stuff since no formal declaration of war has been made according to Hague Convention III?

The US follows the Hague Convention and other 'rules of war' regardless of if the other side does or not.

Re: Military technology: Magic bullets

#39

Post by gvb »

gvb wrote: post #24
__alexs wrote: post #4

Surely it's just a 1 axis accelerometer and perhaps a lookup table or some basic maths? The military sure do like to make themselves seem important. Super secret alien assault rifles being attacked by unspecified hackers from unknown locations. Yep, better keep funding new and exciting ways to kill people.

No. An accelerometer measures change in acceleration. When the round is fired, it will experience a huge acceleration from the propellant along its axis plus a very large rotational acceleration as the rifling spins the round from 0 revolutions per second to a large number of revolutions per second. Once the round leaves the barrel, it is falling at a constant acceleration (9.8m/s, freefall, 0G, "weightlessness"), so…

I got it wrong in my first sentence - in order for an accelerometer to be used, there has to be changes in acceleration proportional to distance travelled. Per the rest of the discussion, there isn't any.
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