Lane's .308 Lightning Build (log)

[Lane]

This is NOT an AR platform gun/rifle. 

No need to read further if you don't care about electric guns. They are universally un-impressive given the current state of technology. 

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I did try to fit this design into an AR platform rifle in my mind; many times. I couldn't find any way to "want" the projectile, or anything else useful to live in the mag well. The forward position of the bolt face is not useful here either.

The only way I see this working is similar to the p90 design. Which follows with a few more design constraints. That flippy magazine is a helpful cue. Most electric guns are built front heavy because of the storage requirements. Electronically fired projectiles need to come from the back of the gun; much like many pistol designs. Ideally; from the butt stock, and following a long barrel. 

Nothing I've seen yet deals with rifling. Even the GR-1 (Gauss Rifle) does not bother to spin projectiles. There are a number of ways to accomplish this without much (or any) sacrifice. I've seen the "motor spins up a projectile" design a few times in my research. That's a fine idea. Feathers. I think I have a solution there already that better still.

The big issue is pulse length, and "grab" so as not to induce any suck-back. Spinning a projectile is secondary (or not addressed at all) in most coil gun designs I've looked at. The further out coils though; should not at all match the coils at the grip/butt stock end. No way to get real power or speed if you don't get stupid on the muzzle end. 

The way to start this is to look at single coil velocity, and then add a second coil; ideally far away, and have optical triggers to present data about that travel time. An external and internal chrono can give the final word (both will be used in this case). Then start adding more.

One thing that really triggered me was some ultra-high-quality designs using aluminum projectiles. I'm not sure what the voltage or current crossover is in that respect. What crazy numbers are required for aluminum projectiles to be useful? This video is of a really different design. A single stage bench mount with 1,000,000A surge. Really. Single stage, unknown (right now; will calculate later)... Single stage 35mm aluminum projectile. Yeah; foreign language. But that argon filled trigatron might be the key here. Seems like it could be smaller. Also; maybe using an external induction coil; but no idea how to manipulate that "through" an acceleration coil. Much to learn...

 

 

Also this abstract. I need to be in the 1km/s range at the least in a handheld. 3km/s would be amazing: https://ieeexplore.ieee.org/document/195657

[unforgiven]

[98Z5V]

This is gonna get Spicy!     I love it...

[Lane]

Had some time to sleep on my project. I'm still mentally preparing for the initial trials which could possibly begin as early as tomorrow. 

I have some old coils in various forms laying around; but I do still need to order magnet wire. Just not sure exactly how far to go with it, thinking 12 gauge isn't out of the question at all (I can use regular jacketed wire to figure that out in the mean time).

That trigatron coil gun was pretty unique, I haven't found much like it. I also can't find decent trigatrons for sale. I'm not a master of lampworking by any means, but it may be possible to fabricate a few. They are very simple devices. Really interesting; is they support extreme voltage and current, and they make a flash when the operate. No need for Chinese made LEDs to make your electric gun look cool; high voltage discharge that's functional is a lot more Sci-Fi anyway... While reading about them, it became apparent that they don't NEED to contain argon gas; air works too with a larger gap, even mineral oil is an option. They can even operate outside of a glass tube, as contacts in free air (bad idea here).

I did spec this project with SCRs (otherwise known as thyristors), as that's what most people use for this type of triggering. I have some on the way, and a few on hand already. The ones I have a rather large, and have an unknown maximum pulse current (no real datasheet). They certainly work somewhere north of 400A@1,000V; wouldn't know for sure without blowing one up with a meter attached. Found some more on closeout with an actual datasheet too. They are smaller; yet support pulses of at least 1,800A@1,800V. That should be fine for early coil stages at least. The trigatron(s) would have to be at the muzzle end to fire one or more final coils at extremely high voltage, and virtually unlimited current based on electrode gap, bank voltage, coil resistance, and dielectric material.

Images: The ONLY trigatron I can find for sale; not enough power for my project. Argon gas is available for preserving wine; which could be used to fill a home-made trigatron (may need to make my own; especially if I want it to be glass and make a nice flash). An x-ray view of the P90 magazine from World of Guns, and the field stripped (since x-ray is confusing there). And a rough cut prototype projectile weighing in at 123.36 grains. 

Final note; and the best news yet. I think the projectiles could fit in a stock P90 magazine. Seems like I can get a 10 round shipped to NY. The only question I have, is whether a P90 magazine has a restriction to loading the rounds backwards. Does it have a reduction in the round spinner for the smaller neck size so they can't spin in backwards (you'd need to load a few rounds to be sure)? Worst case, I'm guessing I could modify that part; but would certainly appreciate being able to use an off the shelf magazine. 

Edited August 23, 2021 by Lane

[Lane]

This is why I ask about the P90 mag loading backwards. These projectiles would need to be a full cartridge width/diameter on both ends, and have no neck. 

Loading a P90 mag with one in each direction is also proof. Do the feed lips ONLY present a problem (or any problem at all)? That's the easiest fix of any. 

[Lane]

Started building... 

While I was waiting for things to show up in the mail, I pulled down a few more disposable camera flash modules I had laying around (from the last time I messed with a coil gun). Five more photoflash capacitors, and some tiny (unusable) step-up transformers, transistors, etc. I don't think a flyback from a TV or computer monitor is out of line in a capacitor charger for the actual lightning gun. 

But then it hit me; when I was looking at the flash tube connections on the circuit boards. That camera flash IS a TRIGATRON. The flash tube itself is; the whole thing is designed to bang a fuckin trigatron. The circuit design should be a breeze for scaling up that part of the build... And initial testing can be done by using a bunch of flash tubes in series/parallel until I know the parameters necessary to build my own for higher current applications. 

I did the dirty deed tonight. Wound a 14 ga coil. Assuming no other losses (which is unrealistic) it could draw 32 megawatts at 990 volts. Yeah; 33,000A. No way that's going to be an SCR triggered coil, so I might as well start messing with these xenon (?) filled tubes. I'm guessing argon is TONS better in terms of an actually useful high current trigatron. I will need to put these in a cardboard box to operate. I will not be shocked at all if the explode on the first shot. In fact. Some trigatrons are designed to be one shot only (not an ideal design parameter here, but noted). 

Capacitors showed up, and; they are kind of big. I knew that though, I bought them surplus for a huge discount. That was the only reason this project made sense. Mocked up some "modules" to see what kind of volume I need to contend with. This is gonna be a fat boy for sure. 

Anyway. The first shot is close to reality. Still waiting on SCRs in the mail, so I might as well test a big bad INSANE current, or at least super high voltage (lower current) on the 14 ga wire coil (and a trigatron). Wiring up a few small capacitor banks it should give me a decent idea what I can look forward to. Also gives me a chance to calibrate a way to measure current peaks and pulse length (at smaller scales, and prepare for things an order of magnitude larger), as well as setup the Lab Radar for short range use again. A BB gun is a good pre-flight check for that part.

I did operate a 1 meter long carbon fiber test barrel as a blow gun with a 123 grain projectile. It shot quite a bit low, but did make it across the room with some force. I'll try to measure that speed too once I get going here. The projectile fit, and and barrel smoothness are superior to anything else I've ever tried before. Picked up some powdered graphite lube to keep the barrel nice during initial testing (seemed to have some inside already). I simply don't know how the carbon fiber will do with eddy currents (suspect it will be better than brass; probably worse than acrylic).

Will post up some pictures later on. Currently in testing mode, and need to organize to show off those things in a logical way. A test rig with a 40" barrel is certainly a sight to see. Excess barrel length isn't useful in this project though, so it will get chopped. I bought two; so it won't be long before I start drilling, slotting, and ultimately cutting down to a more reasonable barrel length. 

 

STILL want to know about loading P90 mags backwards. The 1 10-round magazine I was going to buy disappeared. And I don't want to commit to buying quite yet if I can't use it right away. I might end up 3D printing that part if the commercial product isn't going to work.

[DNP]

You are a mad scientist and I am waaay interested/entertained in watching this unfold. 

[Sharpshooter]

This is just way fun! Looking forward to the next steps.

As an aside, I had a frat brother in engineering school whose dad worked at jet labs on the original rail gun project. According to my frat brother, they ran into problems that the physicists said were impossible to solve — they were up against the laws of physics. So my frat brother's response? Dad said, "we just engineered around the laws of physics." Yup. I like engineers.

[Lane]

On 8/25/2021 at 11:36 AM, DNP said:

You are a mad scientist

Used to work for someone who would often mention, "you could be hit by a bus today". Rather morbid I suppose; and his intent was to get technical people to work together. Mostly so that if any one person left; there would still be some understanding of intricacies. Also; in the right environment, collaboration can spur more appropriate solutions to the same problem. At the end of the day though; I can't be sure I'll actually be here tomorrow. Might as well have a good time exploring while I am able. And as I mentioned before; it's something I actually started building up while I was in college taking electricity and magnetism courses. I might as well finish what I started... 

21 hours ago, Sharpshooter said:

"we just engineered around the laws of physics."

This is a rather important thing to notice... I worked with a graduate student in the physics department in college, whom I didn't even particularly like... But he would spout off little quips here and there; and for good reason. One time he mentioned that he often subbed g=1 when working on complex problems. Not book problems, but trying to find solutions for unsolved physics problems. The reasoning here is it can be subbed back in later, and makes the calculations easier. This is done for a lot of different reasons though; and is often required to take a problem beyond a road block. The problem needs to be restructured from the "textbook version" to one that tries to maximize every other type of input, or minimize all types of loss. Setting static values, and ranges let you do a bunch of quick brain math problems, to seek out a new realm of testing. Same as setting g=1; once you hit a limit, you can set it static and keep working the problem to maximize everything else. Finding one of those limits while building a railgun is the same thing. A significant milestone for sure!

One thing that I absolutely hated about college physics. All the math was a pencil and paper; had to show all the steps . No special calculators. No formula cheat sheets. You had to know everything, and be able to do all the math in your head (assuming you know your times tables). Then write it out on a piece of paper long form. While I struggled like hell with that at that time; I really do appreciate it now. I didn't have a good handle on calculus before I started, so that was actually a challenge taking tests back then. 

I've come to a new hurdle. What... If any; chance do I have using a microcontroller, if I'm going to be blowing off a 20kV capacitor bank at the muzzle end of the gun? There might be some trigger wiring out that far with at least semi-direct connection to the chip. Do I need to get silly with isolation (I think so)? At this level though; I'm willing to tough it out. What "grade" EMP with fry its own gun driver chip? 

Since nobody replied with P90 mag details. I designed a new projectile. Maybe even cheaper to build; but only useful for testing from what I can tell. Shiiit for magnetic coupling given the small diameter tip. Only marginally lighter though; @ 121grains in weight. It can't be faster; but it might save me from blowing a trigatron on the first shot. It also means; I can ABSOLUTELY buy any FN P90 magazine for this build. And use it.

[Lane]

Pictures:

Old capacitor charger (electric flyswatter); looks like it got banged around a bit. It's arcing on the negative terminal. This also answers my question about an arc pulse causing computer/microcontroller problems. Just messing with this on my desk was enough to reset my USB mouse and keyboard repeatedly... So isolation is going to be a must for triggers near an arc discharge. 

Original "final" design. It was just a single one of those SCRs that allowed enough current to flow through the coil and break a window with that setup. 20 ga coil there is wax potted over a brass barrel. Not sure the specs on that, probably 6 turns wide, and maybe 10-12 turns tall. I'll try to get a measure on it later; but it's too small to really do much with on this project. 

Pile of new SCRs and the old for size/style comparison. The screw terminals probably make a pretty big difference in pulse current; pretty sure I could weld connectors to those blade terminals without trying too hard. And a few photoflash capacitors. 

A layout of the new barrels with test coils, along side the other old and new components (sorry for bad lighting).

USPS small flat rate box with 100 capacitors on end. Not quite full, but more than 3/4s. There are four more bags of 100 not shown; and that might not be all I need depending on how things work out (might need a few more to make the numbers work out with series/parallel string counts).

 

Just need to fix the arcing (remove the old capacitor) and set it up to charge some new test capacitor banks. Then I'll be ready to fire test coils with clip leads, and start moving towards the same with SCR triggering. My original setup used to be fired with a household light switch, but between arcing the contacts, and everything else; it was never able to supply impressive current. I suspect even clip lead triggering will be lackluster in comparison to either style SCR. 

Ultimately that capacitor charger will be rebuilt from the ground up to support much faster charging, as well as higher voltages. Though; I was just looking around, and apparently you can get much higher voltage electric flyswatters. I will probably do so; even if only to kill bugs. There's one on amazon for less than $20 with 4,200V charger in it; seems to do 1000:1 off of a standard lithium battery voltage, and is even USB rechargeable. 

Did a bit of reading about high powered rail guns. Seems like liquifying (or at least partially liquifying) the projectile is helpful in terms of getting it to slide smoothly under the pressure required to get good electrical contact with the rails?  

[Sharpshooter]

The last time I saw a box with something like that in it was at the July 4th fireworks sale! It might have had more potential damage than your stuff, but I have faith in your(?) end product. Keep at it, brother. The only people who don't get their names in the history (or patent) books are the ones who quit trying.

[Lane]

Starting off small. Four in parallel. Did my first firings. 

Tried a bunch of times at lower voltages. This last time I fired with clip leads at ~200V. The arc when clipping on to the coil wire is already getting close to blinding (going to need welding goggles soon). Ultimately, I decided it's time to scale up, so the four pack becomes eight. Also made a small series bank that's charging up near 1,000V (gets really slow around 800V, and I'm only reading 900V on that last image). No problem, that's the next real upgrade; to improve charging speed of higher voltage and capacitance banks. The SCRs for triggering are all rated for 1,000V or more, so that's an important milestone -- I can actually start pushing them towards the limits right away.

Aware that some of my wiring might be holding me back at the moment (to thin to supply peak currents). One step at a time. Probably wind a few more test coils and see how it goes before switching over to SCR triggering. Going to need thicker wire, and appropriate connectors to employ the SCRs for the most part. Though I guess I can start off with some stranded wire simply screwed in. 

It might also worth trying to build my own glass trigatron soon, and figure out roughly what gap length I need in air (at a given voltage). Then work towards filling other gasses. 

[Lane]

Had typed up an update days ago, but didn't bother to post it as I was waiting on things to show up; now it's gone. Short of that was:

I took two steps instead of one the other day when testing. Blew up my first SCR already as a result. I had soldered wires to the capacitor bank instead of continuing to use cheap clip leads for the connection; AND swapped in the SCR (previously spark triggering)... Had I continued using the clip leads it would have added about an extra 1 ohm which would probably have been enough to keep from over-current spike upon triggering the SCR. 

Par for the course though. I knew at least one would be expendable. Perhaps more.

Ordered a P90 magazine so I can start fabricating some type of feeding system, and get a handle on the overall layout of the build. 

Two sizes of magnet wire have arrived. At this point though, I need to build a coil winder and be carful about those details. Coil winder needs to have a ratchet to keep the wire from becoming loose if I let go; or at least some kind of brakes to hold it if I need to stop and make adjustments. 

Some shorter acrylic tubes showed up. They are a bit larger in I.D., but I simply want to have a way to compare with carbon fiber in case there is a noticeable loss due to eddy currents in the CF.

Tried to break some glass tubes to make trigatron test units. But so far I've not done well at scoring the tubes (and getting them to crack in the same place). I have a few more to try before I need to order more. I need a really sharp file, though some people suggest chucking them up in a lathe. I did try to test fire in a rudimentary air filled glass tube, and ended up with little copper bits from the electrodes stuck to the glass. I suspect it would be a problem, but only one way to find out. Also cracked the tube further upon firing.

The final piece of the puzzle at the moment seems to be a vacuum chamber to allow me to resin pot the coils (without air bubbles). With such strong forces, the coils would otherwise move and wear out the insulation quickly. Planning to use the same vacuum chamber for another project though; so it won't be a one use item. Still shopping around for that, and the best dielectric resin I can come up with. There is a commercial product for this, but I might be ok with just epoxy or something depending on the available information. Still looking into that as well. Don't need to stress about it until I have multiple coils already wound; so I need to at least start building the coil winder first.

[shooterrex]

Try a tubing cutter for copper tubing for scoring the glass tubes.

[Lane]

4 hours ago, shooterrex said:

Try a tubing cutter for copper tubing for scoring the glass tubes.

Used to have one of those right here; as I had tried it for cutting off 223 for 300 blackout (never worked well at all). I'll try to find it and give it a try. Can't hurt at this point. I can even work on some previously "wrong" glass tubes if I don't mind the potential for blood.

Might as well water my grass, and my liberty trees if I'm going that route...

[unforgiven]

You are a brainiac brother 🍺🍺 

[Lane]

Been reading on and off about what is needed to get this into the next test phase. 

P90 mag should be here in a few hours, so I can start messing with that. Still need to develop some functional attachment and feeding method. Shouldn't be very time consuming once it's in my hands. With a bit of measuring, 3D computer modeling, and some kind of 3D fabrication output; there are plenty of quick prototyping options for that bit.

Ordered a vacuum chamber to pot the coils. Reading about the properties of possible coil potting options; realized I have a new problem... Not even a big problem, but one I need to incorporate into the coil winder. If a dielectric potting solution is measured in kV/inch of thickness; I need to find a way to separate all the coils by enough distance to allow that material to fill the gaps if I want to get silly with the voltages (which I do). This probably means winding each layer and potting them alone, allowing coil wire relaxation even... Then mating those coil layers and soldering the ends together to form the whole coil. Not at all what I anticipated early on; but seems necessary if I want to hit even modestly high voltages. Then the whole unit can be potted under a vacuum. 

At this point 4kV and 20kV still remain pretty acceptable targets (at least for design specifications early on, I do have a 40kV trigger module though). Doesn't that mean I should consider 100kV too? Even the very best potting solution I can find would require 35 mil gap between all coil wires to support 20kV operations (70 mil thickness at 40kV); and I don't even know where to buy that product. I presume I need an even larger gap; as the next best solution is 42 mil.

These solutions are likely epoxy based, and will be very stiff and brittle; so I couldn't pre-coat the wires and then wind the coil afterward. I did find a product on Amazon that can support 20kV at 50 mil thickness. So that's at least an option if I can't get something significantly better.

I will be focusing on the 4kV options up front as a way to work out some of those details before I step up to the big leagues. 

Should still have enough glass to make a few trigatrons. Not 100% sure about my ability to install electrodes into a sealed glass unit though (melting the glass and creating gas tight seal on those metals); especially if I want a vacuum, or alternative gas. I am relatively confident in ionization triggering for this project though... Even have a bunch of test "triggers" on hand. That was a relief, as I had been considering other options like gas pressure triggering (it's too slow and unpredictable). Might still try the gas discharge for fun in some iteration of this build as things progress. There is evidence that blowing the projectile down a tight barrel is helpful (if I could use that pressure dump to my advantage). It could work out in a single stage build with very specific controls in place (though I still doubt it).

Once I have some trigatron tubes to mess with, I can start looking at arc distance in air (inside a tube) for various voltages, and make some adjustments to my goals. Ultimately; it seems like I'll need to be painting epoxy on a lot of the high voltage electronics sooner or later. Still trying to keep this as stupid and simple as possible in the long run; but actual test results will guide the build entirely. 

Still don't have a deep enough understanding of what it would take to fire aluminum projectiles. Don't really want to commit to any design before I shore up that specific detail. There is some chance at least; that it might be ideal for what I'm working with in this build. Do not want to waste a bunch of designs, materials, and testing trials before making a decision... Especially given the really tricky test projectiles I already have on hand.

[Lane]

Couple of quick images to add to the last post. 

Ordered a rotary to use as a CNC 4th axis; and only just a moment ago realized that I can use it as a coil winder as well. It's not super fast, but has a built in brake (holding torque from the stepper), can already "count" the turns, and will chuck up any size winding core I want. Plenty of torque for winding even stiff wire. The rotary unit will also fit inside my laser cutter, so I might opt to do some of the things I had planned on the CNC, with the laser instead. Cutting glass tubing for trigatrons for example should be fast and easy with a laser. 

P90 magazine looks like it should work fine, except the spring inside is extremely tight with the 10 round limiter. Given the simplicity, I might just wind my own new spring, shorter with less push to make it easier to work with. Looks like the limiter would also be a breeze to remove/replace for the full 50 round capacity. Sadly, even without a P90 in my collection; I bet the powers that be would still LOVE to bang me with a high capacity magazine charge if it were known to them. I guess I'll stick with 10 rounds for this build...

It does still call into question; what is a magazine? Is a plain cardboard box potentially a high capacity feeding device? What explicitly defines a container as a magazine? Asking stupid questions because I only intend to fill this P90 magazine with inert hunks of matter. Might as well be a pile of steel balls in a tube. Could a Bic Clic Stic (writing instrument) be considered a high capacity magazine if it contained the original spring, and more than 10 BBs inside? Is the law about intent; or is it loose enough that half the things you can buy in Home Depot could be considered high capacity magazines? Don't worry... Those laws are in place to keep us all extra SAFE. 

[Lane]

Thought I was going to trim the tail of the loaded component shown in the magazine. But started playing with it first. Dropping the baseplate and letting the spring loose enough let me see I was in the wrong. The tip of these needs to be blunted and polished so as not to rip apart the polymer magazine as they ride the elevator.

Picked up some 5/16" steel rod in two different types (sorry for the poop picture quality). Not sure exactly sure what the composition is yet, but I really only care about that once I test them in an actual coil (then figure out what is "special" about that kind of steel). Need to machine them down on the lathe, making the appropriate blunt and rounded point to ride pretty in the elevator; and also a rebated rim in the rear end, maybe with a drilled tail hole as well.

The Unimat lathe has a pass through, I'm pretty sure this fits... I hope so. The 5/16" steel rod does fit snug in the barrel. Just needs a light polish.

The arrow head prototype was just that. A quick sketch prototype I could play with in my hands... That point is a failure here, in this current design. I also want to make new points that are more heavy in the front (shorter rear threads), so I can try a solid aluminum tail as well. Need to cover my bases here. I'll whip up some CAD drawings of each in a bit... Still trying to finish up a quick magazine mount so I can start presenting to a barrel. My current guess is with a bit of compression I don't need feed ramps at all if the point is nice.

So far the magazine is feeding fine with less spring pressure.

[Lane]

Vague 1/12th scale pencil sketch to layout some of the technical aspects of this build. The magazine rides back as far as I can get towards the buttstock. A lot of the "empty" space is going to be crammed full of wiring (like the HV charger, and some basic triggering elements).

Still haven't really begun to figure out how to strip a projectile out of the magazine. There are a lot of options for that. Even a simple solenoid isn't a bad idea given everything else is already electric. Not opposed to making it a manual bolt, or a straight pull action affair either for simplicity sake. Even a spring powered hammer action would be appropriate enough.

I have a reasonable idea how to setup the feed ramp, but I still don't know how to attach the magazine. Going to study a 3D model of the P90 design and try to work it out. There aren't any threads, or ridges to speak of; it just seems to kind of sit in a plain round hole and clip in a notch on the back end... Though; there's a strange 2.5mm offset on one of the rims of the circle. Not sure what that's supposed to do yet.

It appears the spring in the 10 round is the same as the 50 round magazine, which explains why it's so tight with a limiter. Maybe I should just work with it that way for compatibility sake.

Already have a few cardboard models for things like the capacitor banks (so I can get a feel of their size and scale in real life), as well as some CAD drawings. Planning to setup a test bench for this, and might as well lay it out as close to the ideal design as possible. From the business end, it "reads" barrel output, large HV coil, trigatron tube, capacitor banks, physical trigger, smaller pre-launch coil, HV supply, battery power, feeding system, magazine mount, and a pair of steel plates as a safety backstop (in case the projectile goes backwards), then the buttpad. 

A lot of designs use IR optical triggering to determine where the projectile is at a few points, and facilitate timing for triggering. I'm not sure if that's going to work if I'm firing off an arc discharge of any reasonably size. That remains to be tested... I'm not sure if simple opto-isolators will be sufficient, or if I have to work without them. Another method is electric contacts in (inside) the barrel. I'd like to avoid it; but there may be no other choice but to omit a computer/microcontroller from the design entirely. 

If I were able to use optical triggering, I would want 3 of them very close to the final HV propulsion coil. Three; because I need to know a rate of change as well. Gravity (vertical angle of shot), friction from the barrel, and air resistance inside the barrel, are going to be slowing it down (where a gunpowder projectile would be (hopefully) still speeding up at this point in a barrel). 

Some other full scale sketches in the drawing too. I was shocked though; some of my freehand bits turned out to be actual 1:12 scale by "default". Seems like things are falling into place. Just created a cutting document to score glass tubing in the laser. That gives me the ability to start testing spark triggering again in a controlled manner. Vacuum chamber should be here soon for potting coils.

[Lane]

For reference. I don't think I own any shotguns shorter than the max build length here. 

It's going to be heavy no matter what... But that was kind of the point. There is a possible "trim length" shown. The same build specs, with only a 24" barrel (and things compacted more tightly into the design). 

[Lane]

One other thing... Here in New York; I'm not sure about a thumbhole stock... I'm really not sure about any of the laws in relation to this build. Especially if it could be designated as a "semi-automatic". 

It's going to have to be a "Boar Grip". And it might even need to flip out so it could collapse into the design. That's the only way I can see to avoid the thumb hole (as shown in the drawing).

Stay SAFE out there.

[Lane]

Last one for a bit. This seems like the p90 magazine "thing". Getting setup for the laser cutting of this mounting bracket. 

I'll post back once I get it hooked up and working. Looks like 45 degree twist on the upper part, and a solid lower circle for insertion (it will ultimately cut two components, just need to draw them on top of each other for measurement purposes).

[Lane]

Quick update; with a picture. The laser cutting mostly worked for the P90 magazine mount. Things fit, but I designed a few of the parts backwards in my rush. The ring parts needed the square frame, and the locking part needed a rotating frame. Minor to fix. It does help me to be able to see any test these parts in hand, so it wasn't really a loss.

Determined that I was wrong (and should have figured this out before now). A P90 magazine can't be loaded backwards. Any projectiles that need to be magazine loaded will need to be roughly the shape of a full 5.7x28 cartridge (not projectile)... Though, I'm guessing some profile embellishments will be allowed, like boat tailing, and perhaps smoothing the neck transition somewhat.

Found a number of scholarly articles about various induction based designs and testing. From both Army Research Laboratory, and Sandia National Laboratories. Highly technical in some cases, but it won't hurt to review some of the design details as well as outcomes. Still considering the ability to fire aluminum projectiles over steel; which would require that slightly different induction driving setup. I suppose the ultimate determining factor is going to be performance. 

Still wondering; can a hybrid projectile do both? Can I have a steel tipped, aluminum tail projectile firing the same coil in different ways as it travels through?

918254.pdf 45_GHERMAN.pdf 10106476.pdf ADA329260.pdf

[DNP]

On 9/13/2021 at 5:02 AM, Lane said:

One other thing... Here in New York; I'm not sure about a thumbhole stock... I'm really not sure about any of the laws in relation to this build. Especially if it could be designated as a "semi-automatic". 

It's going to have to be a "Boar Grip". And it might even need to flip out so it could collapse into the design. That's the only way I can see to avoid the thumb hole (as shown in the drawing).

Stay SAFE out there.

How do they treat air rifles?  By definition, this should not be a firearm…right?