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Graham said on the 13/03/2018

Paradigm Development part 1


Back in 2006 I was talking to a friend about air weapons, he was very much interested all things shooting related and was very interested in us doing something together as he also had substantial business interest in the Middle East. We decided that the apparent holy grail of the Airgun industry then, was the Single Stroke Pneumatic Rifle, something that could compete with a PCP without the requirement for any separate recharging gear. It was decided that I would develop it and he would assist with funds to keep me going whilst I did it.

 

I had, had some thoughts on the matter from several years back and was confident that it could be done. However I should mention at this point that several companies had tried to do this previously and had either gone bankrupt or very nearly lost the companies in the process. I also understand that Daystate sunk quite a substantial amount of funds into trying to produce a production version of such a weapon too.

 

There were some designs produced with varying degrees of success:- John Bowkett produced a number of Single stroke Pneumatics I have seen a few JB 1s and I am sure there were others but I think they may have went under the Titan name. In the mid 1980s Richard Spencer designed and produced the Air Logic Genesis; this was in my opinion one of the very best and I think around 175 were made. In the 1990s Parker Hale ventured into the Air gun market with the Graham Bluck designed Dragon rifle and I gather around 2000 of these were made but reliability became the main problem with that one.

 

In all of the above cases the cocking load was very high and considered to be a real problem by many potential customers. So much so that no one else bothered to try again for several years because everyone would disregard it as too hard to cock. Whilst I had had an idea back in the mid nineties of how to do it, I decided to wait until it felt like the time was right and hopefully this was it.

 

And now for the first of the technical bits! I know from the work that I did with Brocock back in the air cartridge days that in order to produce 12 ft lbs of energy at the end of a 400 mm long .22 barrel it requires 120cc of air compressed into a 0.6cc space I.E.200 bar pressure. This assumes that there are no losses due to heat and that the air is released directly behind the pellet. However in most cases the barrel is situated above the power tube and this means that the air is released from below and that is not a very good transfer port path for efficient propulsion of the pellet. This tends to mean that more than 120ccs of air is required to be compressed. Furthermore in order to compress the air to 200 bar a piston load of 1061.85 kg is required assuming a piston of 26 mm diameter and a gap between the piston head and valve face of around 1.2 mm. The cocking force comes from the need to overcome a load of more than one ton and that is a fact that cannot be changed, or can it?

 

Over the next 12 months I tried various different designs of pump system to try and produce a full power single stroke rifle without having too heavy a cocking load and whilst it is easy to produce a rifle of around 6 ft lbs of power getting anything over 10 is not as easy. It can be done but the cocking load is significantly higher. I started out using the Crows foot type of leaver as it was used extensively for cocking crossbows in the middle ages and is a very efficient type of leaver.  However one of the real problems with producing a full power single stroke rifle is that it requires a very long stroke to compress the necessary volume of air. If we ignore the effect of heat and friction etc. Initially there is very little pressure required as you have to go half way to increase the pressure to 2 bar then each time you half the distance between the pump head and the valve unit the pressure doubles. This means that the pressure really shoots up in the last few milimetres and the accuracy of the final volume is paramount to performance, 0.1mm of the stroke can make a real difference.

 

Now Let me run a couple of basic ideas by you; 1 if you blow up a paper bag and close the top with your hand, when you release it, it will drop to the floor. However if you blow up a balloon when you release it, it will fly around the room until empty. This started me thinking, that if I could have a container that would hold the air at pressure so that when the trigger was fired it would force the air out as it contracted, we could then perhaps use air at a lower pressure and this would be considerably easier to compress in the first place. But what pressure should we use?

 

Well that brings me to idea 2 if we consider a normal PCP rifle and as the pressure in it decreases the hammer system usually opens the valve further which causes the power level to increase until the air pressure in the container is too low to give sufficient velocity to the pellet at which point the power starts to drop off. From experience I find that rifles will perform quite well down to about 70 bar pressure before too much velocity is lost. I therefore decided to use 70 bar for my pressure setting and this has the advantage of dropping the necessary cocking load on the 26 mm diameter piston to 371.65 kg a mere 35% of what is required to produce the original 200 bar pressure that everyone else has to use. This is why my rifles are much easier to cock. Futhermore, at this very low cocking pressure, I am able to put needle roller bearings in the pivot points which also helps with cocking but this cannot be done on much heavier loads as the bearings crush. 

 

When I started I produced a rough action to prove that my calculations of volume were right, they were but the cocking load was horrific as expected. I then set about trying alternative ways of achieving the same results without the huge cocking load. This involved designing and making a series of test bed units until finally I found the right one. This took me 3 years of sweat and toil as I was determined to produce a minimum of 17 ft/lbs of energy in .22 in order to give myself any hope of producing a .177 rifle capable of anything near 12 ft/lbs. However that is another story and I will address that one at some other time.

 

At the end of the first 12 months I had produced this rifle but whist it performed well giving around 9 ft/lbs in .22 and 6 in .177 with a fairly easy cocking stroke it became obvious that it would never be capable of giving the performance I was eventually looking for. However at this point my backer decided that it was going to be a long job and dropped out, so from here on in, I was on my own.

   

 

Some of you may find that the information I have given here is enough to produce something that will work but it will not work nearly as well as it would, if you contact me and purchase a license to make it and I then supply you with a full set of working drawings and instructions plus all of the necessary help required to make it work properly. 


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More in the series ...
From Humble Beginnings
Reaper Development Trail
Paradigm Development part 2
Paradigm Development part 3
Whirlwind CNC Rifling Machine
Air Shot Gun Development


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