WELCOME TO THE AIRCANNON PROJECT... LAST UPDATED: 07/OCTOBER/2016
SINCE IT IS ILLEGAL TO PURCHASE AIRGUNS OVER THE INTERNET OR VIA MAIL-ORDER IN THE UK ( FROM RETAILERS- PRIVATE SALES ARE NOT AFFECTED ), AND I DON'T DRIVE WHICH MAKES IT VERY HARD TO GET TO ANY PHYSICAL RETAIL SHOP, I DECIDED IT MIGHT BE A LITTLE BIT OF FUN TO MAKE MY OWN AIR WEAPON :D
I decided to go with an all-metal aircannon since it is far less prone to failing under pressure and doesn't rely on glue to hold it together. I also wanted to build something that could fire airgun pellets, so an all-metal cannon that could handle higher pressures was the best option.
All parts used are off-the-shelf brass and stainless steel couplings, along with a pressure washer handle, air rifle barrel-blank, silencer & adapter, and picitinny rails for mounting sights and a small bipod. the only 'machining' I will need to do is enlarging the bore of one of the couplings to accept the 16mm diameter barrel.
PLAN A: .25 CALIBRE AIRGUN BARREL
As we can see, all the parts came in eventually and I fitted the barrel into its coupler- I forgot to take a picture of it assembled as I was too excited to test it.
As it happens though my excitement was short lived as it turned out the power output was only slightly higher than that of my 'real' Air rifle, around ~13ft/lbs vs 11.9ft/lbs ( 12ft/lbs is the legal limit so I made sure not to put in as many pumps after that, using my airgun pump for charging the cannons tiny 'air reservoir'- I have a chronoscope to check velocity and calculate power ). The larger calibre of my 'cannon' is no advantage in this situation as you ideally
need around 25ft/lbs of power for it to be effective in .25 calibre for hunting and long range shooting, anything less and you will find the accurate/deadly range of the pellet falls way short due to lack of power behind it.
I decided to go back to the drawing board and came up with a new plan, which is actually my really old plan before I got the airgun barrel idea; I swapped the airgun barrel for a 19mm inside diameter aluminium pipe, so that I can fire empty Co2 cartridges ( technically speaking they are actually empty nitrous oxide cartridges from my place of work, but identical in size and shape to Co2 cartridges so anyway... ).
PLAN B: 19mm ID ALUMINIUM BARREL
I re-used the drilled out 1/2" BSP nipple and ground the threads off of one half, allowing it to slip inside the new barrel which has an inside diameter of 19mm, then epoxied it in place; I made the mistake of using an empty apple juice cartoon to mix the epoxy on, which resulted in the ink being dissolved and turning the epoxy green, oops.
I added a couple Picitinny rails to give me somewhere to add a sight and a hand grip eventually- probably going to use a red laser sight so I can aim from my shoulder and fire from the hip too.
At this point I'm thinking about the tiny air reservoir and ways to make it a little larger without introducing any extra parts which will increase the chances of leaks; I'm still dealing with one which I cannot cure- it seems not all BSP fittings are created equal, I ideally need to use some couplers which accept Dowty seals, like the ones for my Air Rifle stirrup pump hose and filling adapter.
So, more research and a few tweaks will be coming, along with a sighting system and fore-grip, maybe a shoulder-stock too so stay tuned...
With regards to ammo, I have 3 types that all work rather well; a 18mm steel ball, empty 8g Co2 cartridges with a few wraps of electrical tape, and an old brushless motor rotor. The steel BB fits really well so just a single layer of tissue paper to act as a wad creates a good seal, very powerful and accurate round. The Co2 cartridge is pretty light so range and accuracy isn't as good,
but I had a couple dozen of these & they didn't cost me anything, so they make for fun rounds. The old BL motor rotor is a near perfect fit without any wadding or tape, makes for a vicious projectile though I make grind off the the shafts as they aren't needed in this application. None of the projectiles cost me anything and all work quite well with my limited testing so far,
looking forward for a chance to do some proper testing against layers of cardboard to see how well each type of ammo penetrates and such, need to build a test stand to hold the card...
PLAN B: CONTINUED- OTHER BARREL OPTIONS
Since the last update I purchased a short vertical grip ( and installed it sideways, naturally ) and a cheap laser sight ( which works extremely well as it happens ), making aiming from the hip much more practical ( shoulder aiming being impossible so no other real option ).
Not wanting to be limited to just one size of ammunition, I decided to make a couple new barrels, one with a 9mm bore, one with a 23mm bore; I purchased a small lot of mouse balls with a 22.5mm diameter which make for nice, heavy ammo and do a lot of damage, inspite of having a rubber coating.
Ideally I wanted to remove the rubber coating and use the balls just as plain steel balls, but the coating was very hard to remove, and the diameter without it was rather odd so no suitable barrel could be found. I didn't opt to just buy plain metal BBs as they are rather expensive- unlike the 9mm ball bearings
I bought which were rather a lot cheaper, no concern about losing those after firing them ( using a safe back-stop at all times regardless, but small BBs are easy to lose all the same ).
At the moment I'm just waiting on another laser sight and I will then have two barrels with grips and sights- the side mounted grip feels a lot better when hip firing, enabling me to hold the cannon nice and low with a firm grasp. Soon enough I will post some testing videos and damage photos.
TEST RESULTS, 19mm BARREL
Due to the size of the projectiles I needed to upgrade from my trusty old Crombo CB-625 Mk4 chronograph, so I flogged it on ebay and picked up a nice new Shooting Chrony F1; I naturally modified it a little bit by adding some LED strips on top of the diffusers
so that I could use it indoors- no desire to pay the insane price they wanted for a couple 40watt pygmy bulbs in a plastic box that you're meant to use for low-light shooting. Anyway, with the modifications completed I set about testing the various projectiles to record average
velocities, and from that compute the power ( in ft/lbs ) based on the weight of the projectiles ( in grains ). As you can see from the results above, the large 19mm projectiles produce a decent amount of power given the fairly low velocities, compared to an airgun pellet for example
( my air rifle has a muzzle velocity of around 900-1000fps based on the particular type of pellet I am using ). I still need to test with the 23mm and 9mm barrels, I will put those results up in due course so stay tuned for more...
TEST RESULTS, 9mm and 23mm BARRELS
Results are in for my other two barrel/calibre options, and I'm a little disappointed with the power level of the 9mm steel ball ammo, though it shouldn't be a surprise either really for anyone who understand the basics of ballistics.
In order to increase the power output with a lighter projectile, I would need to increase the velocity, and that means using more than ~1000psi. Fine in theory, though chances are the O-ring seals will fail with pressures much beyond 1500psi- I will need to do some more testing
and perhaps try some different seals; flat rubber washers would be far better compared to squashed O-rings. At any rate, that's the first round of testing completed and I'm pretty happy so far, I will have a couple weeks holiday in a month or so, and provided it doesn't
rain the whole time I will be able to go somewhere a bit more isolated in order to do some destructive testing against various 'hard' and soft targets. I'd do some of the testing in my flat, but the chances of debris or ricochets causing damage to walls or windows is a bit too great, along with the noise the cannon makes.
PLAN C: AIR BOW ( AIR CROSSBOW )
Happy with the performance of my cannon, I was pondering other things I could fire out of it when I started noticing that so-called Airbows ( air powered cross bows ) were becoming quite popular, so I set about doing some research into barrel and bolt sizes.
I picked up a cheap set of five 16 inch crossbow bolts, carefully removed the plastic Nock from the rear ends and measured the inside diameter of the hollow aluminium shaft, which was 7mm. After a bit of searching around I found a few retailers on Ebay selling 7mm aluminium and brass tubing.
I bought a 30cm length and a 1/2 inch BSP to 1/4 inch hose tail adaptor, filed down the ridges on the hose tail section and epoxied the brass tube into place. The tube was a tight fit inside the crossbow bolts initially as there was some glue inside bolts from where the Nock was glued in place,
so I used a small file to clean up the inside lightly, and polished the brass tube with some fine wet & dry sand paper, then a scotch-bright pad. Two of the bolts had glue right down inside them that I simply couldn't reach to clean away, even after trying some White spirit to dissolve the glue,
so those went in the scrap metal box sadly, leaving me with three good crossbow bolts.
TEST RESULTS, AIR BOW WITH 21 GRAM BOLTS
I have now done some test firing and have results worth sharing. With the standard field tips, the bolts weight 21 grams or 308 grains, and at 1000 PSI they travel at approximately 171 feet per second, resulting in a power level of around 21 foot pounds. When the canon is pressurised to 1500 PSI, they travel at roughly 211 feet per second resulting in a power level of 30 foot pounds.
This is pretty good for such light weight bolts, though it is worth considering that a production 'airbow' can fire bolts at around 400 FPS or higher- I think the limitation I have is the volume of air and the pressure, since I really have no idea how much a real airbow uses in either case. I could increase the volume and pressure easily enough though there is already a tiny airleak at 1500 PSI- such is the issue with using multiple couplings to act as an air reservoir, hence usually sticking to 1000 PSI.
I will do more testing as the weather improves and I pick up some new arrow heads which are heavier and more exotic, and hopefully will get some test photos and video against various targets...
UPGRADED AIR CYLINDER
LASER SIGHT AND MOUNTING PLATE
I had made plans to do some testing on privately owned land in a fairly rural setting ( this cannon is a little loud to be testing in an urban setting- given the nature of incidents recently it's wise not to risk having the police turn up on your doorstep if it can be avoided... )
, but those fell through so I'm waiting for another chance fairly soon. In the meantime I decided to do a little bit of work on the cannon and upgraded its air cylinder from 3/8" BSP fittings to 1" BSP fittings, roughly tripling its capacity per shot ( now requires about 30 pumps to reach 1000PSI vs 10 pumps previously ).
I have also decided to mount the horizontal grip directly to the new cylinder with some jubilee clips and a length of picatinny rail. Final job I did was to build a mounting plate for the laser sight on top of the main plastic body of the cannon, I used a piece of L shaped aluminium and a short length of picatinny rail bolted to it, then glued the assembly in place with lashings of epoxy resin.
Just for giggles, I found some nice heatshrink tubing with a grippy pattern and added it over the barrels, mainly to hide the ugly seam running down the barrel where I had to split the outer tube and glue it in place with JB Weld. I still need to do some testing, the weather refuses to cooperate ( sunny when working, raining when not ) and it's getting very busy at work due to peak season approaching. We'll get there eventually- I really want to make some videos of it destroying stuff...
NEW FILLING VALVE AND PRESSURE TEST
I've been closely following the work of Joerg Sprave on Youtube ( for a very long time- awesome channel, go check it out ), specifically his insane 1000 Joule arrow launching air cannon, or airbow I suppose. I noted with interest that he uses a one-way
check valve for filling the air cylinder, an item intended for use on hydraulic systems and is rated for upwards of 3000psi pressure. Well, the craptastic filling valve on my cannon was only ever intended for 150psi or there abouts, and seeing as I stripped
the threads on the bit the lever screws onto, and the fact it leaked around the threads, I elected to pick up one of those nice check valves myself- not too expensive and surprisingly heavy too ( always a good sign ). I installed it using a couple Dowty seals
and tested it by pumping it upto 2000psi, twice the normal pressure I operate at. No leaks detected, and now I feel much happier about going even higher- I'll never reach the crazy power levels Mr Sprave is achieving, owing simply to the type of projectiles
and size of his air cylinder- I have searched and searched and not managed to find much info or examples of steel pipe with threaded ends; I would need 3/8" BSP in about 30cm length, somewhat hard to find as it turns out, but my current solution seems to work just fine regardless so I'm not too worried like that.
In an interesting side note, I was looking at updated Home Office guide lines regarding Firearms Legislation, and found a few rather delightful loopholes surrounding air-powered weapons. Namely, any items designed to only be fired underwater ( harpoon guns for example ) are excluded from existing rules concerning power levels,
likewise any item designed to throw out rope, such as a rescue line ( essentially rescue equipment intended to fire a projectile with a long length of rope attached ). In addition, paintball guns are also excluded ( provided you are only firing paintballs out of them, kekeke ), and air cannons not designed for firing solid projectiles- such as confetti cannons and t-shirt cannons.
Very useful information as I'm sure you'll agree...