airgun, air rifle
There are a number of disadvantages with the traditional airgun design
1. The pressure build-up behind the projectile is gradual and slowed by the long and indirect path of the gas resulting from the geometry of the system.
2. The projectile starts moving forward before the full pressure built-up; increasing the volume of the gas and resulting in lower propelling pressure.
For best results the full gas pressure is released instantaneously behind the projectile without the time delay of the gas flow path. The projectile should, as well, be fixed in the firing chamber until the full pressure built-up.
This is exactly what this design is all about. Shown here are simplified flow trajectories (velocity) of the air flow in both cases
Air flow trajectories in a conventional airgun
Air flow trajectories in this design
So how is this achieved? In some way it is not a new idea. Burst, or rupture, elements were proposed and used to launch projectiles. The idea is simple; a thin diaphragm inserted behind the projectile designed to rupture at a certain pressure. The rupture, once initiated, is very fast and the gas volume behind it free to move. This is a standard technology used in safety valves.
Rupture disks are used in various pneumatic launchers. Hobbyist use them in potato (spud) guns and researchers in light gas guns. And there are a number of patents covering various applications including projectile launching, for example US5365913A, shown below.
The problem is that none of those systems are easily implemented in a target or hunting rifle. The diaphragm must be inserted separately after the projectile and sealed and secured (bolted flanges, in the patent shown) and after firing removed and replaced. Many applications use a number of disks, the burst trigged by pressure change between them. Air rifle users need a simple system that in loading and shooting does not differ from regular operation of the gun.
The solution is an integral rupture element, part of the projectile itself. So the innovation here is actually not the gun, but the bullet. The rupture element can be formed as part of the projectile and from the same material, or it can be attached to it during fabrication (US patent applied for).
In the photo below the projectile on the right is machined out of brass and lead filled, a form of a full metal jacket bullet. In the middle is a lead bullet with a steel disc cemented to the base. On the left is the burst disc after firing.
Below is a short video showing the experimental setup and the testing. Those are the first steps in the development and still long way from the final design.
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