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Coil Rifle (not really a rifle, no rifling)? Answered

so, I've been considering modifying an inexpensive muzzle loader into a coil gun with a backpack power supply.... it seems to me that this would be possible but impractical, which is perfect for an art installation... I would then take it hunting, to test its lethality. any thoughts on the idea?

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NachoMahma (author)2008-04-16

. I have to agree that it's impractical ... but it does sound like fun! . Lessee: . The smaller the caliber, the lighter the bullet, the easier to accelerate. . That's a lot of ampacity in the backpack. Insulation, insulation, insulation. Especially the cables feeding the coil. . Probably going to be a lot of heat generated by the coil. . Wouldn't the ferrous barrel "shunt" the magnetic field?

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tech-king (author)NachoMahma2008-04-16

1) the power supply needs to be a capacitor bank and a battery, not one large battery or something 2)the bullet cannot have a sharp point, making it useless for hunting 3)the metal barrel would rob considerable power.

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gschoppe (author)tech-king2008-04-16

I already considered the barrel issue, and would need to replace it with something non-ferrous... In terms of hunting, a round pellet from a shot gun will perforate a bird, and a 22 caliber bullet doesn't deform much at all, so I'm not sure why you imply that a point would be necessary... what I need is a high muzzle velocity and mass of projectile, with a reasonably low cross section presented to air resistance... however, a larger, pointed projectile would function better for a kill... Why couldn't I accelerate a ferrous cylinder with a pointed tip down the barrel?

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badideasrus (author)gschoppe2010-09-30

what do you mean a 22 doenst deform? most of the 22s i have are hollow point, and they mushroom into bowls almost, dependant on what you hit with them. they also fragment into practically nothing.

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tech-king (author)gschoppe2008-04-16

a pointed tip deprives the gun of power. it is mass that needs to be accelerated, but cannot accelerate itself. in short, it steals momentum from the projectile. i have never hunted, so i cannot say if a point is necessary. however, adding one would lower the fps.

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NachoMahma (author)tech-king2008-04-16

. Not sure I understand what you mean. If the tip is made of ferrous material, it should receive energy along with the rest of the projectile. . For hunting bullets, the point improves aerodynamics (more fps at impact point) and penetration.

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tech-king (author)NachoMahma2008-04-16

id have to look up the exact saying, but the point does not receives as much power, however it still weighs something. unfortunately, the ratio of lost power to lost weight is not the same, so you end up losing power. although the aerodynamic improvement is a good counter argument. it might even be better to have a point (get it?). ill look it up; in the mean time, use a point, but be careful.

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gschoppe (author)NachoMahma2008-04-16

however, the lighter the bullet, the lower the penetration and range (in air) lots of insulation will be a must, for a LARGE capacitor bank and several lead-acid batteries will be used.... I'm talking about a hiking pack filled to a maximum 100lb capacity (what I can carry long distance without killing myself)

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NachoMahma (author)gschoppe2008-04-16

. Ek = (mv2)/2 Need I say more?

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gschoppe (author)NachoMahma2008-04-16

well, you may be saying it takes more energy to accelerate a larger mass, or you might be also saying that velocity has more effect on imparted energy than mass does... i guess you do need to say more I agree fully, obviously (I'm not going to dispute a basic law of physics), however, lethality is more than just imparted force... the cross sectional area of the wound, its depth, its placement, and its smoothness all play roles in lethality... in general, I would think a larger, slightly slower bullet would be better for lethality

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tech-king (author)gschoppe2008-04-16

that would give it more stopping power, but less penetration power. thats why high stopping power sidearms are often .45, and the armour piercing rounds of the mp7 are only 4.7mm nato.

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gschoppe (author)tech-king2008-04-16

I'm not sure about the mp7, but some of your best armour piercing rounds are hollow-point depleted uranium, so as to be very dense, and to deform so as to present a large cross-sectional impact, but before deformation they present a small cross section in the barrel, so as to maximise muzzle velocity. (correct me if I'm wrong, this is from vaguely remembered discussion with an buddy of mine who was a marine)

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NachoMahma (author)gschoppe2008-04-16

. Most AP rounds are specifically designed for minimum distortion (mushrooming) to facilitate maximum penetration. Wikipedia has a good article.

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gschoppe (author)NachoMahma2008-04-16

ah, you've got me there, I'm mixing up two types of ammo... hollow point and Armour piercing.

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NachoMahma (author)gschoppe2008-04-16

. I don't look at it as "getting" you. . Yes, penetration, wound channel size/condition (raison d'etre for hollowpoints), &c; are ALL important, but they all rely on kinetic energy. For a general-purpose gun, speed is king.

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badideasrus (author)NachoMahma2010-09-30

you know, none of you are takeing into account magnetic saturation. the larger the bullet, the more magnetism it can absorb before it is saturated, which is very important in multi-stage coil guns.

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Kiteman (author)gschoppe2008-04-16

They keep the narrow cross section on impact, increasing penetrative force-per-unit-area, but after that deformation and fragmentation is highly desirable for maximum destruction within whatever you penetrated.

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killerjackalope (author)Kiteman2008-04-16

Yes desirable for maximum destruction within what you penetrated... I never thought you were one for dirty talk I already realise how childish that was but c'mon...

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NachoMahma (author)gschoppe2008-04-16

. The kinetic energy goes up with the square of the velocity. Increasing the speed of your projectile will improve lethality more than than decreasing the weight will harm it. . Yes, penetration is important, but a smaller CSA (especially at a higher velocity) will penetrate easier.

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lemonie (author)2010-04-28

Why? For the sake of doing it?
(Chemical-power is best for rifles.)

L

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badideasrus (author)lemonie2010-09-30

i would agree, exept that the navy is building those huge railguns that supposedly can shoot over 200 miles.... at like mach 8

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gschoppe (author)lemonie2010-04-28

Precisely for the sake of doing it...  Entirely impractical but wondrous applications of scientific principles are an obsession of mine.  Its why my cell phone and camera charge via induction (custom homemade battery replacements with the same footprint), why my home lighting is internet accessible (custom controllers and passworded server), and why I want a carrier pigeon with a programmable rfid embedded in him.

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kelseymh (author)gschoppe2010-04-29

Sounds like you'd make a great physicist, and a terrible applications engineer :-D

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lemonie (author)gschoppe2010-04-29

That's a perfectly good reason, I use it myself a lot of the time...

L

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gschoppe (author)2008-04-16

also, would it be better to have a longer hollow 'bolt' than a solid 'pellet'? i'm thinking that exposing a larger area perpendicular to the magnetic field would increase the force on it, and (maybe, I can't remember if this applies) the shell effect (like with gravity) would keep the inside of the pellet from receiving any impulse at all

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NachoMahma (author)gschoppe2008-04-16

. I would think solid would be better for a DIYer - if your field is not symmetrical, a tube is liable to collapse. My gut feeling is that a tube would perform better, if you can keep it intact. . I gave away all the literature I had on coil guns (mainly EE journals) to one of my daughter's friends (engineering student). . BTW, from what I've read, coil guns have a tendency to tear themselves apart (often catastrophically) and "vaporization" of the projectile can be problematic. Be careful.

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Jackus95 (author)NachoMahma2010-04-28

I think you mean a rail gun can vaporise projectiles. Coil guns have no contact with the electrical current. 

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NachoMahma (author)Jackus952010-04-28

.  Contact is not required. Anything that puts that much energy into an object (not all the energy is turned into motion, some gets turned into heat) will cause it to heat up and possibly boil. Microwave ovens heat with no contact.

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Jackus95 (author)NachoMahma2010-09-29

Yes but that would need a massive power source

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Kiteman (author)NachoMahma2010-04-29

Yup - the good-old eddy currents.

Regarding solid vs hollow, why not a magnetic tube filled with a non-magnetic solid?

Maybe a steel tube filled with lead?


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kelseymh (author)Kiteman2010-04-29

I think you want something both non-magnetic and non-conductive.  The moving mass is going to see a changing magnetic field, which will induce eddy currents in a conductor (and lead is good enough to be used as solder, after all :-).  NM's idea of a solid hardwood plug, or maybe a refractory ceramic, seem promising.

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NachoMahma (author)Kiteman2010-04-29

.  It sure sounds like a good idea. Your filler would either have to stick to the tube under acceleration (lead should meet that requirement if it doesn't melt). Or at least one end of the tube would have to be crimped/closed (crimping doesn't sound like a good idea). But I'm no engineer - electrical or mechanical.
.  Lead may be too malleable to resist collapse if both ends are not sealed. Think toothpaste if only one end is closed. Just a guess.
.  There should be something that would work. Heck, a (well dried) hardwood plug and some Elmer's glue might do the job.
.  Shouldn't be too difficult to press fit a magnetic tube over a non-magnetic metal (stainless steel?) rod. Might need a little bit of silver solder to make sure it stays together under acceleration/heating.

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kelseymh (author)2010-04-29

Besides the standard "slug down a pipe" design, somebody recently posted in Answers describing a coilgun (or perhaps a version of a railgun) which used a barrel with internal stages, and a hollow cylindrical projectile.  I could imagine doing the same with a rifle, after taking the forward sight off the barrel.

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gschoppe (author)kelseymh2010-04-29

perhaps possible, but I think a ferrous barrel would still interfere with proper operation... i think the whole gun has to be a custom job... with the exception of the stock and butt

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