Saturday, 31 May 2014

As real as I can (legally) get it

Here in the UK gun laws are (rightfully) tight. However blank firing replicas are legal. I was asked last year to develop a Lasertag system that detects a blank round being fired, and sends a Lasertag pulse in response.

My first challenge was to detect the firing of the blank. Initially I developed a circuit which used a piezo sensor to detect the shock from the blank. However this was very susceptible to noise and was unsuccessful.

My second attempt utilised a neodymium magnet attached to the rear of the Glock slide. This, in conjunction with a Hall effect device encapsulated in a 3D printed mount within the carbine kit. The recycle time of the Glock replica was about 70ms as timed with this jig:

Here the hall effect sensor is mounted behind the Glock blank firer. Checking the timings on my scope showed this:

Tweaking the software to only shoot when a pulse of approximately 100ms or less prevents shot packets being sent when a human cocks the gun. There is no way a human could pull the slide back and release it in 100ms.

This allows maximum realism. The only way to fire a Milestag shot is if there is a blank up the spout. When the clip is empty, it must be physically reloaded before anther shot can be fired.

Looks pretty good when fitted to the carbine kit with 3d printed focus tube and a small project box from ebay. Both are fitted to the picatinny rails of the carbine with 3d printed fixings.

However....multiple shots through the carbine kit resulted in it's destruction..and a trip to the doctors for an X-Ray. We only managed to video one shot...with a following misfire. Proved the concept though..Watch this space...

Update 3 Jun : Some people have expressed concern as to the safety of the blank firing replica. I'd like to point out that the barrel is physically blocked with a plug of titanium and falls under the none licensable category of replicas under UK law. (See below).Absolutely nothing comes out of the barrel when the replica is fired. All the chemical energy does is make a bang and cycle the slide.
They are loud, and hearing protection is preferable but nothing, no projectile or wadding or even gases leave the muzzle.

UK Law on blank firing replicas:

"What are Blank Firing Weapons?

Blank firing weapons generally fall into two different categories:

Those not requiring certification

These are imitation firearms, not readily convertible into a firearm to which section 1 of the 1968 Act, as mended, applies. These "firearms" are not firearms within the definition of section 57 (1) of that Act, and therefore are not required to be held on a certificate. (see "What are imitation firearms?")

Such weapons are capable of firing, or capable of being adapted or converted to fire, blank ammunition. With blank ammunition no shot, bullet or other missile is discharged from the barrel - you just get a "bang" and maybe a puff of smoke.

Such weapons are often used in battle re-inactments, theatre and TV productions and for starting races."


Cabe said...

Very interesting work! Although I might have considered using a gas air-soft pistol for prototyping work, less chance of A&E trips :)

Tony said...

Indeed! But this literally is the optimum bang for buck ratio. Also, the business model allows us to sell the blanks a la paintball style....