I'm currently building a world in which coilguns are the primary ranged weapons. Technology is advanced enough to allow for portable high velocity coilgun weapons. I'm assuming the projectiles fired from these weapons will have velocities roughly similar to modern firearm velocities.

I like the idea of a sort of "force field" which will only block the ferromagnetic projectiles fired from coilguns. My question is could some form of electromagnet be made to trap coilgun projectiles before they hit their target, similar to how that mech suit from District 9 catches bullets? Or would something like that just attract bullets straight into the user? I assume the electromagnet device will have the ability to detect projectiles moving above a certain velocity toward the user, and thus only activate when necessary.

If you have any alternative suggestions for stopping ferromagnetic projectiles those are welcome as well.

Since I'm not too concerned with exact mathematical equations for this, I really just want to know if something like this is possible if the only limitation is the laws of physics. We can basically assume unlimited technological and energy resources since I'm more than willing to fudge the numbers for "rule of cool".

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    $\begingroup$ defelecting bullets by different means was tested a lot by mythbusters. You may want to take a look there. And while i'm unable to do the math, i'm pretty sure the answer is 'no way' $\endgroup$
    – Burki
    Jan 12, 2018 at 9:16
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    $\begingroup$ I was positively sure that we had questions/answers dealing with such a concept already, but now I can't find anything really fitting. Go for it! $\endgroup$
    – dot_Sp0T
    Jan 12, 2018 at 9:29
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    $\begingroup$ If you assume unlimited energy and technology (and you don't care about collateral damage in the slightest) you can use the principles of induction to deflect, stop or vaporise even non-ferrous bullets $\endgroup$
    – Joe Bloggs
    Jan 12, 2018 at 9:30
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    $\begingroup$ We're assuming the technology to create compact high velocity coil guns but not told exactly what that is. If the technology was used in reverse, a bullet fired the wrong way down a second coil gun, could it not slow the bullet down sufficiently? $\endgroup$ Jan 12, 2018 at 10:28
  • $\begingroup$ @dot_Sp0T You may be thinking about the questions from a certain user that went into a similar direction like this one $\endgroup$
    – Secespitus
    Jan 12, 2018 at 10:36

2 Answers 2


Mostly useless

If such a field would exist, you simply need ammunition made of a ferromagnetic sabot with non-ferromagnetic projectile.

That is a steel shotgun shell with lead pellet or slug. 19th century technology makes your super high tech force field obsolete.

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    $\begingroup$ Reminds me of the replicators in Star Gate. They were immune to energy projectiles, but not lead slugs. $\endgroup$ Jan 12, 2018 at 21:37

Use another coilgun.

Your coilgun accelerates the projectile by triggering electromagnets in precise sequence and increasing the velocity of the projectile. You could catch the projectile in a coilgun the same way, in reverse: each electromagnet decreases the velocity of the projectile.

The trick is to catch the projectile within the coils of the deceleration coilgun. If the trajectory of the incoming projectile can be calculated this could be done by a computer.

I like this because on slowing completely, the projectile will be sitting at the bottom of the deceleration coil gun. Switch the sequence and fire it back!

If your computers are good, this will become a game of catch between the coilguns. You would need to figure out some way to put spin on the projectile or otherwise defeat the trajectory calculators of your opponent.


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