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New Gauss Rifle

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Simon

Wed Mar 29 2006, 01:44AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

If we're quoting resources, don't forget our wiki.

Some people have non-solid projectiles to avoid eddy currents (not an area I've investigated myself).

I just find a bolt/nail/screw that fits well inside the coil, cut it to size with a hacksaw and shape it with an angle grinder. Anything along those lines will result in a decent enough projectile.

rupidust

Wed Mar 29 2006, 02:08AM

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Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
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Posts: 85

You can try fabricating the projectiles for yourself and hollow pointing the tip. But hollow pointing with basic tools takes a long time. Gauging does reduce eddy currents but also removes mass. For every gram removed is 1/2 a joule lost given that the speed is the same. Hopefully speed does increase to compensate loss of mass and added speed to bring up efficency. In my opinion, if one does not fabricate a few slugs of different lengths and compare the energy result of those rifled to those non rifled, then why does one make a slug in the first place.

Text and Image quoted from ACG-
"I use steel rods from common hardware stores. Measuring, cutting and pointing the raw steel bits is a fast process, about 2 minutes a projectile. However, 2 minutes feels like 20 when being inundated by the loud noise, sparks, and heat generation associated with forming metal. Polishing a projectile to a crystal shine, now that consumes a lot of time. Below is the systematic process I use governed by the tools I have.

Measure and mark the rod sections to approximate projectile length. Cut the rod into raw sections with a saw and metal cut off blade. Grind one end of the raw bits into a point shape with the raw bit inside drill/driver and metal sanding blade inside saw. Press the raw bit onto sanding blade at desired point angle while bit and sanding blade rotate in counter directions. Remove any excess length of this bit by grinding down the non pointed side with a saw and sanding blade. Polish the projectile using a drill press and sand paper. Alter projectile point angle with the coarse 60 grit sand paper. Buff the coarse finnish with the 220 grit sand paper. Apply the final shinny coat with the very fine 600 grit sand paper."

Quantum Singularity

Wed Mar 29 2006, 03:08AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I had an idea and I was going to wait and see how it turned out before I announced it, as I am not sure how well it will work. But it will save time and hassle making your own projectiles and only require 1 small cut (easily done with dremel and cut-off wheel). My idea was to use commonly available field points from archery. They come in a few different shapes, sizes, and weights, but of most interest will probably be the largest 'bullet point' ones available. They are already precesion made, and I beleive out of high carbon steel. The only issue I see is that they are lighter and rather stuby and not as long as what most people here use. But maybe for designing a compact hand held pistol they may be ideal? The only mod you haev to do is to cut off the small shaft that exits from the rear of the point. The sizes I have in the picture are probably the largest ones available, 145 grain bullet points. That I believe is equivelent to 9.4 grams and will be a bit less after removing the stem part. They are 5/16" diameter. Archery shops normaly sell them for around 20 cents each if I remember correctly.

Fieldpoint

Edit: I beleive the larger one on the right is 145 grains, the others are 125 grains (8.1 grams).

Remus

Thu Mar 30 2006, 06:10PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

To Quantum Singularity:
The points Ive seen are hollow on the inside in order to attach them to the arrow. I'll have to check out these solid arrow heads.

@rupidust:

That sounds like a great idea, I'll give it a try. I might have to go and buy a grinder tho, how much do those cost?

@Simon:
Thats exactly what I was trying to do, based on various coil guns made by other people, Ive seen that rifling the bullet adds to speed, and reduces Eddy Currents. I'll try both rifled and non-rifled, once I get my coil gun finished up.

whats the average weight of a projectile in grams? I suppose if I just chop a piece of steel thats like 2 or 3 inches long, then measure the weight, that would work, but of course Id like to get an idea.

Before I forget, does anyone have a schematic of a charging circuit for the capacitor bank. I dont want to go waste 8 bucks on a camera just to strip out its guts. Id rather build it myself anyways, so I can custom build it for size. maybe solder some smd's rather than full size resistors/transistors. Thanks.

Quantum Singularity

Thu Mar 30 2006, 06:37PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Remus wrote ...

To Quantum Singularity:
The points Ive seen are hollow on the inside in order to attach them to the arrow. I'll have to check out these solid arrow heads.

The only hollow heads I have ever seen are for glue on type old fasion wood arrows. Any sporting goods or specialty store I have ever seen usually stocks exactly what I have in the picture above, atleast in the U.S. (not sure about mars though)

Again I dont know how ideal they are, but it would be an easy way to get a bunch of identical bullet shape projectiles with minimal fabrication.

I plan on trying the 125grain bullet points but I am focusing more on an induction coilgun for now. The reluctance cg will probably be later on this year.

Rifling... not sure how well this would work. For one thing for rifling to actually spin a projectile it has to be under high pressure against the riffling. Any drag on a small coilgun would probably kill its performance. There are ways to spin it ahead of time and launch it already spinning. I would worry about building a working gun and then trying to improve upon it. Good luck and hope it works out!

EDIT> I might have missinterpreted what you meant about riffling. Riffling is usualy a helical groove cut in the barrel. I think you simply mean slotting the projectile, which should reduce eddy currents, increase speed & efficiency (slightly).

Remus

Thu Mar 30 2006, 06:50PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

Quantum Singularity wrote ...

The only hollow heads I have ever seen are for glue on type old fasion wood arrows. Any sporting goods or specialty store I have ever seen usually stocks exactly what I have in the picture above, atleast in the U.S. (not sure about mars though)

Yea, I dont know what to call it.

a helical groove cut but in the bullet, not the barrel itself...two birds with one stone...reduce Eddy currents, and increse the speed.just slotting it might reduce eddy currents, but it wont necessarily increse the speed or efficiency. The more arodynamic the projectile is the better the efficiency, or at least that what I understand of it.

rupidust

Thu Mar 30 2006, 07:01PM

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Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
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I do not think you need a grinder, never used one myself. The main advantage of self fabrication is choice. If your coil and cap arrangement match an exiting projectile like an arrow tip, thats great. But for experimentation you need to alter diameter, length, material, and tip till its just right. Raw rods of varing diameters and lengths can be gotten from Lowes, Home Depot, Ace and local shops easily and just one rod will produce more slugs then you will need, all for couple of dollars, assuming the pre-existence of tools of course. Pointed tips penetrate easier, flat tips hit/push hard but do not penetrate at lower energies, and hollow points do both, penetrate and hit hard.

Remus

Thu Mar 30 2006, 07:06PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

rupidust wrote ...

I do not think you need a grinder, never used one myself. The main advantage of self fabrication is choice. If your coil and cap arrangement match an exiting projectile like an arrow tip, thats great. But for experimentation you need to alter diameter, length, material, and tip till its just right. Raw rods of varing diameters and lengths can be gotten from Lowes, Home Depot, Ace and local shops easily and just one rod will produce more slugs then you will need, all for couple of dollars, assuming the pre-existence of tools of course.

So how do you make the tip like that?

Ive got a dremel, will that work?

is this the right charging circuit to be used? Flash camera charging? <br>

mod edit- oversized picture- and don't forget to credit the source, Sam's Repair FAQ

Quantum Singularity

Thu Mar 30 2006, 08:05PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Rupidust is quite correct saying the main advantage of making it yourself is that you can make it any shape or size. The possibilities are endless if you are skilled and have the right tools. I am definately going to try my field point idea just to see how it works though. There are so many variables in a cg that you need to start somewhere, mine will be the size/shape of the projectile being fixed, and I'll design from that point on. Reducing eddy currents with slotting will reduce losses and possibly make it faster and more efficient. The riffling or slotting itself probably wont make it faster or more efficient due to spin, as its unlikely to spin very much. With heavier projectiles it takes alot of force to get spinning, and I doubt air pressure will make it spin very much under a few hundred meters/sec. FWIW I just determined my rifle shoots bullets that spin 857 revolutions per second. Even if you had fins on you cg projectile I doubt it would spin more than a few revs per second.

And about hollow point projectiles... usually this is to increase the expansion rate of the soft lead / copper jacket bullets. That wont happen on a solid steel slug. It might look cool though. If you want maximum shock transfered to a target with solid steel than a flat nose would be best, and pretty easy to make (might not even have to do anything).

Remus

Fri Mar 31 2006, 07:35PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

well based off of one of the other coil gun sites, and their experiments, Id have to stick wth hollow point. The normal projectiles went through a can, but the hollow point projectile, went through it, and tore a section out of the can along with it. Im thinking of developing coil guns for hunting...so anyways that my view of the hollow point.

I still cant find where to get some steel rods from, anyone know?

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