electric rifles have become practical

=military =chemical safety

 

current primers in ammo

In a rifle, the firing pin strikes some lead styphnate or lead azide primer, which explodes, igniting the propellant. The primer is small but lead is quite bad so being in an indoor firing range is somewhat unhealthy.

I don't like lead pollution, so I spent a little time thinking about alternatives. (This reminds me, the USA is still using leaded aviation gasoline, despite alternatives existing.)

 

 

existing electric primers

Modern autocannon ammunition (eg 30mm for the M230) is sometimes electrically primed, using a spark to ignite nano-thermite which ignites the propellant. Could the same thing be done in a rifle cartridge? Technically, yes, but it would be expensive, and the energy required for ignition is higher than is ideal. Also, those can be sensitive to shocks from static electricity.

There was an electrically-primed rifle made commercially, the Remington EtronX. That uses a 9V battery to resistively heat a pellet of normal lead primer until it explodes. That can be done faster than a firing pin, but we'd prefer something faster than resistive heating. And of course, they produce lead pollution. Also, the (9V) battery was only good for 1500 to 2000 shots - you've gotta pump those numbers up, those are rookie numbers. Yes, a lithium-ion battery would last long enough, but we'd still prefer less energy usage.

 

 

semiconductor bridge initiators

A relatively recent development in initiators for military items is the semiconductor bridge initiator (SCB). A small silicon chip is made so that at a threshold voltage it suddenly makes a tiny explosion. They can be made so they require very little energy to set off, yet are resistant to electrostatic shocks. And they can trigger medium-sensitivity compounds such as PETN. See avalanche breakdown for how they work. Originally, SCBs were considered too sensitive to static discharge; here's a paper describing how that problem was solved at Sandia.

SCBs are small and use old process nodes, so they can be cheaper than the cheapest microcontrollers. There are bad microcontrollers available for under $0.10 and a mass-produced SCB could probably be made for $0.03 or so. Semiconductor chips used to be too expensive for rifle cartridges, but that's no longer the case...if you make enough of them to amortize millions of dollars of investment over cents per round.

 

 

advantages

The above system has several potential advantages over current (firing pin + lead primer) systems:

 

1. There's no delay from physical movement of a firing pin, so firing would happen faster after a trigger pull.
2. Electronic triggers have more design options. They'd be the same for bullpup and conventional rifles. Multiple triggers could be linked - for example, a foregrip trigger that's held, and a capacitive sensor that triggers firing when touched if the foregrip trigger is held.
3. Cartridges wouldn't need a separate chamber for primer, because it wouldn't need to be crushed. That could make them slightly simpler and lighter.
4. Not needing a firing pin assembly means a rifle can be slightly shorter and less complex.
5. This primer wouldn't produce lead vapor or particulates.

 

The potential disadvantages would be:

 

1. It would require a battery — but the battery would last for >10k shots.
2. Cartridges could be more expensive — but it should be possible to mass-produce the primer assembly for under 10 cents, which is similar to current primer costs.
3. The new rifle and cartridges wouldn't be compatible with existing ones. So, it would make sense to introduce it when a military decided to switch to a new cartridge — like the .277 Fury. Of course, that's not going to be electrically primed...but it could have been. Well, maybe the US Army will decide the .277 Fury is too heavy/expensive/loud and try again, or maybe China will follow the same reasoning as the US Army.

 

 

lead primer replacement

If you don't want electric rifles, are there any drop-in alternatives to lead primers? Yes, and several have been used, but past attempts at replacing lead ones had some reliability problems. Currently, the leading candidate seems to be KDNP; it seems fine to me.