Static electricity question

[rdmallory]

I have been reloading for about 1 year and have primed over 10,000 cases by hand using my RCBS hand primer.

Last night while priming .223 rounds I had a (PMC) primer go off when I was removing the shell from the hand loader. It has been very dry in the house lately so I am guessing it was static electricity. It left a nasty black mark on one of my fingers and I now have an ammo can with 1999 good rounds and one dud.

What does everyone else do to prevent setting off primers with static electricity?

Doug

[Mike Irwin]

Your best bet is to maintain proper humidity in your loading area, 50 to 60 percent relative humidity.

[LaserSpot]

How could static set off a primed case? I'm sure the shell would shield the priming compound from any discharge. Live ammo isn't affected by static electricity.

[B.L.E.]

How could static set off a primed case? I'm sure the shell would shield the priming compound from any discharge. Live ammo isn't affected by static electricity.

A agree, the brass case and the brass primer metal forms a Faraday cage around the priming compound. It was probably something else that set off that primer.

Here's a link to the best faraday cage demonstration I could find.

http://www.youtube.com/watch?v=e4WAuGf6fsY

[LaserSpot]

Cool video!!! So, what else could have set it off?

Do any of the remaining rounds have high primers?

[rdmallory]

None have high primers, and I always seat firmly by hand so I can feel when it bottoms out. What was strange was that it was already seated and I had just reached up to slide it out of the shell holder when it went off. There was no pressure on it at the time. It is mixed brass that has had the pockets hand reamed and ever now I miss one or two that has glue or a crimp not fully removed but I can tell then as it is hard to seat the primer. I have actually crushed a primer that caught the lip up the case I have not seated all the way in and it not gone off.

I dropped it into the ammo can when it went off and I went through most of them trying to find it and all looked normal to me.

They are PMC primers made in Russia but I would not think that would of made a difference.

I no longer hold my finger over the end of the casing when removing it.

Doug

[LaserSpot]

That's pretty hard to explain. My best guess would be a hang fire from a defective primer or primer pocket, but I hope someone has a better idea.

[rdmallory]

"Not a soul touched the gun. There was no dimple in the primer cap. The gun recoiled off the nightstand and landed on the floor, fully cocked and with a new round in the chamber.

I had the shell casing examined in the crime lab. They determined the primer was not fully seated, the powder was cold and static electricity had arched on the cap setting it off."

So if there was an air gap where the primer was seated it has happened before.

Doug

[LaserSpot]

Sounds like a lame guess from the crime lab, that's not something they can determine through tests or examination. I can give some reasons why it couldn't have been static electricity:

There is no source of static electricity (like friction) inside an assembled 45 ACP shell.

There is nothing inside a 45 ACP shell with enough capacitance (your body has capacitance, for example) to hold enough static charge to produce a spark.

There's no insulating barrier (like an air gap); any static charge that was generated would be dissipated by the conductive brass before it could build up.

If there were a static charge inside the case, it would take the path of least resistance, this would be the wall of the case. It would not be through the flash hole, through the anvil, and through the priming compound.

[rdmallory]

That makes me feel a little better. Hate to carry round 2k of .223 maypops.

Doug

[wncchester]

No static charge differences can exist across a metallic object, the charge will be equal at all points. When any two metal pieces are firmly connected together, such as a primer in a pocket, the primer cup is effectively the same as the rest of the case. No way I can visualize any static charge leading to that detonation, almost certainly has to have been from some other cause. What? Dunno.

[T. O'Heir]

Whatever caused it, it wasn't static electricity. Most likely a high primer.

[Sport45]

I now have an ammo can with 1999 good rounds and one dud.

Why did you toss the one that popped in with the rest? How big of an ammo can does it take to hold 2000 .223 cases? I know a 50-cal can will hold a few hundred '06 but I've never seen how many smaller cases they hold.

[amamnn]

apparently some people were sleeping in HS science class-- they might want to go back and learn the differences between ferrous metals and non-ferrous metals especially as concerns the conduction of electricity. And if they do not-- I hope they will be haunted by the ghost of the sky police lieutenant who gathered up a box of unfired rounds as souvenirs on the Gila Bend AZ gunnery range, slid them across the seat of his car, and was quickly and terminally chastised when the rounds were set off by---wait for it---STATIC ELECTRICITY---the finding of the accident investigators. I was there.

I use an anti static mat on the top of my bench. They can be had on the internet. The prices are a lot less these days.

[LaserSpot]

learn the differences between ferrous metals and non-ferrous metals especially as concerns the conduction of electricity.

OK, what is the difference? They are both conductive enough to attract a spark, or dissipate a static charge.

ghost of the sky police lieutenant who gathered up a box of unfired rounds as souvenirs

Do you believe in ghosts? I haven't heard of this incident, but the opinion here has been pretty unanimous that once it's assembled, fixed metallic ammunition isn't sensitive to static electric shock.

[rdmallory]

Sport45

When the thing went off I just dropped it and it ended up in the ammo can with the rest.

I prime and store all my brass in sealed plastic ammo cans because I prime off the loader.

[DG45]

QUOTE: "Learn the difference between ferrous and non-ferrous metals..."

Well many of us try to learn things from this forum without going back to school. So, could someone please explain the difference between a ferrous and non-ferrous metal and give some examples of each type of those metals so we hoi poli will know what the heck you mean?

I don't want to hijack this thread, but this question occurred to me as I read this thread because I'm looking at buying an old antique 12 gauge priming tool for reloading black powder shotshells. Looks like old heavily patina-ed brass, but magnets stick to it. Should I buy it for my intended purpose? Should I worry about whether it's ferrous or no-ferrous?

[TheNewGuy]

Anyway, all I know about electricity is that it travels the path of least resistance to the ground, and that the switch on the wall being in the off position is no indication that the wires in the fixture aren't flowing with twitchy goodness. Took me a few times to figure that one out, and a few more for it to sink in.

I'm curious for someone to explain the physics of how static electricity can ignite a cartridge. I'm not saying that it can't happen, but it seems highly improbable. It would seem to me that electricity would flow around the case or pistol, as in the other poster's example, and not through the primer cup and case.

Unless there was case lube/dirt around the primer (more resistance) as it was being seated and a little static build up was on the little nubbin that pushed the primer in the case and a finger touching the case completed the circuit. I guess that's possible. It definitely seems more plausible than setting a pistol down for a few seconds and having it discharging it's static load all by itself, enough and in the right place to fire a round. That one sounds more like ghosts up to shenanigans or something.

I would definitely be interested in a little more education on the subject if there is anyone else out there willing to share.

[LaserSpot]

In this context, ferrous means iron, or an alloy containing iron.
Examples: cast iron, carbon steel, stainless steel

non-ferrous just means a pure metal or alloy that doesn't contain iron.
Examples: brass, lead, aluminum, titanium, beryllium-copper.

When a steel wrench is dropped on a concrete floor, it can create a spark. This can be a problem if you're working near flammable vapors, or in a combustible atmosphere. Because of this concern, OSHA requires the use of non-sparking tools in hazardous environments. Non-ferrous alloys can be used to make non-sparking tools. This means that they wont generate spark from impact or friction (like a dragging car tailpipe does).

This doesn't mean that non-sparking tools made from non-ferrous metal won't conduct an electric spark; this may be a point of confusion. Both types of metal conduct electricity.

The anti-static mat is a good idea when you may have loose powder, primers, or priming compound on the bench; other than that, I didn't find amamnn's post to be very informative. There is some more discussion of static electricity in this thread: http://www.thefiringline.com/forums/...d.php?t=391093

[Sport45]

Another thing to remember is that electricity flows on the outside of a conductor. That's why a stranded wire can handle more current than a solid wire for the same voltage drop. A static arc striking the outside of a cartridge will stay on the outside. To ignite the primer or powder the arc would have to originate inside the case.

In this instance I believe snapping the case out of the shell holder caused a high primer to strike an edge and go off.

Thank you for sharing the story as I have learned from your mistake. I've been putting my finger over the case mouth when taking primed cases out of my Auto Prime. I won't do that anymore.

When the thing went off I just dropped it and it ended up in the ammo can with the rest.

I probably would have too. It's pretty hard to hold onto something that just bit you.

[Shawn Dodson]

Static electricity? No. If you're holding the hand primer then you and it are the same electrical potential. No electrostatic discharge (ESD) will occur because there is no electrostatic differential between you and the metal tool.

In addition, the moment you grasp a case to install into the hand primer any electrostatic differential will be discharged and the case will be the same electrical potential as both you and the hand primer.

[Mike38]

QUOTE: Another thing to remember is that electricity flows on the outside of a conductor. That's why a stranded wire can handle more current than a solid wire for the same voltage drop.



I disagree, or I don't understand what you're saying here.

For example let's go with 12 awg copper conductors, one stranded and one solid. Both are fused at 20 amps. Both are capable of 25 amps. Both have the exact same circular mills of copper. Both weigh the exact same per foot. As seen by electric current, they are the same.

Electricity is the movement of electrons threw a conductor or path. In a copper wire, stranded or solid, all of the electrons move, not just the ones on the outside.

I'm an Electrician by trade, and yes, I've been wrong before.


As for the original poster, I believe your problem was static electricity. Ground your press. Do not ground it to an outlet. Do not ground it to a water pipe. Use an isolated ground. A ground wire firmly attached to the metal frame of the press, straight outside to a ground rod directly driven or burried in the ground. No interuptions, no splices in the wire, one solid piece straight to ground. Then you have to wear a ground strap on your wrist, connected to the ground wire, so the potential is the same. All that, or humidify the room.

[Unclenick]

He's either talking about high voltage, where the charge repels itself out to the surface, or about about alternating current skin effect, which only becomes a concern for normal wire sizes at frequencies in the tens of kilohertz and up, and for which the added conductivity is only slight in standard strands, because they increase the wire surface area. Litz wire, which has individually insulated strands does a bit better.

Ferrous metal has iron in it. Non-ferrous metal does not. Ferrous comes from the Latin for fur, because smiting your enemy with iron weapons was thought to put hair on your chest.

As to the Faraday shield, most of us who've been in instrument design depend on them. They have a shortcoming, though. Many a shielded piece of electronics has been blown when its shielding chassis was struck by lightning. The electrical field in that instance is so great that the momentary difference between the voltage at one end of the shield and the other, as the electrical field propagates over the surface, can induce damaging voltages on the enclosed circuit. Devices in danger from lightning or other strong electrostatic strike often require double Faraday shielding, with the inner shield tied to just one point in the outer shield. That attenuates the damaging induced voltage considerably, though not 100%. Under some extreme conditions even a tertiary shield may be required.

Cartridges are pretty safe. They are not easily fired by static charges. It is possible for an electric discharge to fire a finished metallic cartridge by heat, if the spark is strong enough or plays on the primer long enough. It is also possible, theoretically, to hit the primer with charge so fast it drives an arc from the cup to the anvil via capacitive charging, but it takes some serious juice applied very, very rapidly, indeed. Accidental static discharge will not readily fire cartridges, or they would go off spontaneously in aircraft all the time.

[Sport45]

For example let's go with 12 awg copper conductors, one stranded and one solid. Both are fused at 20 amps. Both are capable of 25 amps. Both have the exact same circular mills of copper. Both weigh the exact same per foot. As seen by electric current, they are the same.

I was speaking from memory and I last thought about this in '79 when I was taking college physics. Something about the charge always being on the surface of the conductor. Maybe it was a frequency thing with A/C currents and skin effects. It made sense at the time and I passed the course at any rate.

Do the two cables you mention have the exact same capacity or just the exact same rating?

[dmazur]

Another electrician here -

The ampacity (capacity) of a conductor depends on its end area, which can be expressed in circ-mils. For a 12AWG conductor, stranded or solid, the ampacity is the same.

As another mentioned, when you get into high voltage and/or high frequency, skin effect and other nasties pop up and the rules change. For typical low voltage (< 480v) applications, I understand solid/stranded ampacities are the same for the same gauge.

Also, ampacities are determined by things like temperature rise, so "rating" depends on which design table you are using. Obviously, a conductor with a resistance of only a few ohms is capable of carrying currents far in excess of its ampacity (rating), but it is considered a fire hazard at that point...