I have only 'discreetly' tested firing my air rifle prototype out of a window in the workshop, but it is a frightening creation, because it makes big holes in the targets I've temporarily attached to the trees to the south, and they are 15 mm thick solid planks. The back just splinters, and I can shoot through more than one plank. I wanted a lot of bullet energy, but I can honestly say I underestimated how deadly this weapon would be, but then I hadn't thought the tanks would have such high pressure, which is one reason I made them 1 litre, 1000 cm3. An seagull that unwisely landed and annoying screeched from my target tree turned to mush and feathers long before I reached the much higher energy the bullet now has, and the bullet I use is short with less than half the weight it can have. In order to not waste a lot of good thick planks/targets, and to recover and reuse the lead, I had help moving one of the bullet stops from the firing range, which is thick angled sheet metal that hangs behind targets and directs lead and lead shrapnel into a barrel of water. Unfortunately, it's not the least bit discreet to shoot at, so I had to tell people I'm experimenting. The target and barrel is very noticeable from Jane's window and more, so obviously she gets I'm experimenting with some kind of weapon related tech. Iselin, whose questions I promised to try to answer, has been pleased to know I'm working on a potential weapon project.

  A big advantage of these air gun successes, is that my oxyhydrogen firearm project is on hold. Very high air pressure in a cylinder is potentially dangerous, but still so much less worrying than oxyhydrogen to produce, use, store and carry around.

  The barrel is similar to that of hunting rifles, and this is simply because a larger heavier bullet is easier to give high energy, especially with compressed air. Energy calculation, i.e. Joule, is the square of the velocity in metres per second times the weight in kilograms divided by two. If the weight of the bullet doubles, the energy doubles, but if the speed doubles, the energy quadruples. Also, black powder is a chemical combustion that creates gas, while compressed air is compressed gas that has to expand from a container under decreasing pressure through a valve and a relatively narrow pipes. So the bullet diameter can't be too big as it consumes more air and requires more flow. Going from 12 to 16 mm in diameter is an area-volume increase of 78 %. So, due to flow and volume, it makes sense that it is easier for a compressed air fired projectile to reach 100 m/s than 200 m/s, which will have four times more energy, and higher velocity means everything becomes more critical with flow and valves, and efficiency will decrease with increased velocity. Expansion also cools down the air, thus reducing the pressure. As the muzzle velocity approaches the speed of sound in the barrel, other problems arise, especially on air flow through narrower pipe sections than the barrel might be supersonic depending on where the gas expansion takes place, and the bullet passing the sound barrier becomes even more of a problem. Just like energy, air resistance also increases with the square of the velocity, so a faster bullet encounters more air resistance and loses energy faster. Finally, air consumption will also be a balance of how many shots can be fired before the pressure drops too much.

  The design I chose is relatively simple and efficient, as I don't want to have the main valve in the tank which would have been the absolute easiest design, and I also want to be able to experiment with pressure regulation. So the high pressure tank/flask is the buttstock that screws onto the long cylindrical shaped block, which internally has a smaller pressure chamber followed by the main valve in the centre, and a hammer. The hammer is cocked and strikes the firing pin on the main valve in the internal pressure chamber, and air flows up to the barrel where the bullet waits. A simple lever moves the barrel forwards and opens up the breech so that a bullet can be pushed into the barrel, and the lever then moves the barrel backwards and locks and seals it. So, the high pressure tank screwed onto the cylinder block with the barrel directly on top, gives a fairly nice straight line optimised for easy flow directly up and into the barrel from the internal pressure chamber, with maximum channel diameter equal to the barrel diameter, and minimal restrictions and sharp corners. The trigger mechanism is screwed directly to the block, and the whole block mechanism is mounted in a gun shaped wooden block with a pistol grip, so the whole thing almost feels like a long barrelled home made paintball marker, but the air tank sits above the pistol grip, and there is manual loading of shots and cocking of the hammer. So it feels like a firearm, and the wooden parts as well as a leather tube around the buttstock air tank insulate skin from cold metal.

  The air pressure in the tank plus low spring force the air tanks own valve shut and seals the tank, and once screwed onto the block, the tank's valve automatically opens and air flows through a drilled hole and fills the block's internal pressure chamber. The harder the hammer hits the main valve's firing pin, the more air comes out of the pressure chamber, and flows up behind the bullet. However, the shots will lose velocity as the pressure in the tank drops because there is no regulation of the pressure, only a restriction of the flow through the narrow drilled hole to the internal pressure chamber. My plan is to test with pressure regulation installed in that drilled hole. Manual feeding also means that the 'long' time to fill the internal pressure chamber does not matter. As a safety thing, the hammer is blocked from hitting the main valve when the barrel and breech are not closed. Overall, a relatively simple mechanism that works. But as I have made a stronger and stronger hammer spring or tensioned it more and increased the weight of the hammer, the muzzle velocity and target damage has only increased, and I have made the internal pressure chamber larger. I'm glad I made muzzle threads on the barrel, because as expected it's loud, and the goal was to try and make something deadly but relatively quiet and user friendly. So I've been able to make a suppressor that lowers the noise, because the gun is just less loud. Lower noise than a suppressed hunting rifle with subsonic bullet and the shot is hearing safe, but it is not silent, and the suppressor is nice. Especially as I shot from windows, and also indoors out through a window.

  The only estimate of bullet velocity, is sound measurement from firing to the bang of the target being hit, and a bit of maths subtracting the time the sound took to reach the microphone, gives me how long the bullet took to travel to the target. It's not the muzzle velocity, but absolutely useful. I just passed 800 joules with a 12 mm calibre 35 gram lead bullet at 214 m/s, and I can reach higher energy with this prototype, or just make a variant with a larger pressure chamber-main valve-hammer, or increase the bullet weight. A lighter bullet will be faster. This is absolutely a lethal weapon. However, I still need to test how the bullet effect is on a body, and a body with different types of armour such as leather, chain mail and plate. There will be many tests. My initial goal was something equivalent to a pistol in energy and shot quantity, with more shots the better and preferably 20 to 30 shots, similar to a MP5, Uzi and Thompson. Those are proven dangerous enough for a lot of combat use in war. A rough estimate of a modern calibre's bullet weight by roughly bullet profile, calibre and density of lead, and subsonic or slightly supersonic velocity, leads me to estimate that a 9x19 mm cartridge has about 400-450 joules, and a .45 ACP has about 450-500 joules, and historically very common Walther PPK and similar pistols probably only have around 200 joules. So 800 joules is 'not bad', and double what I was hoping, and this air rifle shoots heavier bullets that will retain energy better at distance.

  A normal bow for hunting or combat doesn't even do 100 joules, so it's not all about the joules, but also what is shot and how the projectile damages a body, and how it transfers its energy in the body. But I wanted to try how high energy I could reach, and the amount of shots I get from an air tank, because now there has to be a trade-off. What is the best balance between bullet energy versus how many shots it gives? 350 Joules feels adequate and seems to give 30+ shots, but what is too low energy to use against normal armoured targets and be practical? Because each shot has decreasing velocity too. Well, almost. I found an unexpected effect that with a new air tank, the bullet velocity gradually increased before a peak is reached and the velocity starts to drop, which seems to be due to the hammer not having enough force against max pressure on the main valve, and thus not opening as much as it should. Of course it's unregulated pressure, so I've actually wondered if a regulator is unnecessary, but I assume it helps at longer distances. I'm hoping that the air rifle with a regulator will be able to hit relatively predictably and consistently at 150 to 200 metres.

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  The air tank takes far too long to pump up, and if this is to be a practical firearm, so I really need to decide what muzzle velocity is appropriate in relation to the amount of shots it produces and the energy of the shots I want-need. The air tank is interchangeable, but each air tank weighs 3.5kg, and is quite large. I may have oversized the 1000 cm3 tank, but I was counting on lower pressure. At the same time, I don't want to make a smaller pressure tank, because if I make a shorter pressure tank with the same material thickness and diameter and just shorten it to get the weight down to 2.5kg, it will only have about 750 cm3, with the equivalent fewer shots. Given how much the total gun will weigh anyway, which I estimate to be about 2.0 to 2.5kg more than the air tank, it seems more efficient to have that 1kg extra weight and 33% more shot. It would almost be worth going up a bit in diameter and adding 1kg to the air tank, and getting 1500 cm3. A 4.5kg firearm with 750 cm3, or a 5.5kg firearm with 33% more shots, or a 6.5kg firearm with 100% more shots? However, the 4.5kg weapon user can carry an extra 2.5kg tank for a total of 7.0kg, but the weapon is still lighter and more comfortable to carry and shoot. It's not nice to carry around a heavy weapon for a long time, but at least having most of the weight in the buttstock is much better than front-heavy. However, I suspect that a larger tank gives a few more shots more than just the volume indicates.

  In the end, I can simply make air tanks in different lengths and weights, where the user can decide. The tools we made are for 90 mm diameter, but the length of the tank is completely flexible. Making 750, 1000 and 1500 cm3 tanks can be useful for different purposes. In the future there will probably be tools for more diameters too.

  Bullet weight has a big impact on performance, because a lighter bullet will reach higher speed, but have less energy, and be less air consumption efficient than a heavier bullet. However, it is possible to make a hammer that has two power settings; the first power mode gives lower bullet energy with more shots, and the second power mode gives higher bullet energy with fewer shots. A third intermediate mode would also be useful. Or I could just introduce a variable restriction in the flow up to the barrel. Like a small ball valve that gradually closes to give lower bullet energy and power. Some kind of plate with holes would be more consistent than a ball valve, but must be able to seal with the tech restrictions that are here. Regardless of how the power limitation is done, it can be a fairly effective solution to be able to shoot two different types of bullets; a lighter round ball or a short slug for more shots around 350-400 joules, and a longer heavier bullet for armoured targets or larger animals such as horses etc. The choice of bullet also affects the weight of what the user carry, as a long bullet weighs about three to four times more, and a lighter bullet is thus three to four times more shots for the same carried weight. A hollow point bullet that is about 1.5 to 2 times the weight of a round ball is probably the most effective all-round bullet and the least weight to carry. Maybe with some of the heaviest bullets for heavily armoured enemy targets, horses or just hunting larger animals.

  It is common sense that an airgun takes advantage of the advantages airguns have over flintlocks, which is one reason why the airgun will have magazines and repeating action, and be built mostly in marine brass instead of steel. Brass is a bit heavier, and some parts need to be thicker if they are to withstand pressure or be subjected to forces, but apart from the air tank, there are far lower pressures involved than in black powder, and with marine brass, rust and salt water are far less of a problem than with iron and steel. A flintlock weapon must be protected from moisture and water because of the black powder, but airguns don't really care. A firearm that can even be swum with to cross a body of water and still be ready to shoot, and is relatively easy to maintain, have a clear advantage. Then it's just smart to design so that the airgun's most important internal parts are kept free of particles that can clog valves or sliding surfaces, while what is external and movable like the magazine, should be able to handle some dirt etc in the mechanics. Cold and icing require their adaptations. Maintenance and mechanical reliability requires its own. A nice trigger that does not feel spongy, and has adequate resistance and sharp break requires its considerations.

  Before I do any more experiments, though, I need to make an high pressure air compressor, because the air tanks are getting empty and I'm not going to pump them up by hand. I could ask the bodyguards or Hrappr to do it, but I don't like asking someone to do physical labour because I'm too lazy or don't want to waste time on it. A small high pressure electric compressor shouldn't be too hard to build, and I don't mind if it takes a couple of hours to fill an air tank with that air compressor, as long as I can build the air compressor into a box and make it relatively quiet. To keep track of which air tanks are filled and which are used, a flat wide piece of red-coloured leather has been tied around the necks of the air tanks. One side of the leather piece has been given green fabric, and turning the green fabric out indicates that the air tank is filled, and the red-tinted leather side indicates that the air tank has been used.

  I expect the bodyguards will love future air rifles that are less noisy than other firearms, and with a magazine of 8 to 10 rounds and probably pump-action, the air rifle can be fired very quickly. The black powder rifles will have higher bullet energy, and are faster to fire if I include the total time to hand pump up the pressure in the air tank, but air rifles actually have the potential to be a better military firearm than my black powder flintlocks, bows or crossbows. Sure, there are problems with maintenance and filling air tanks with hand pumping takes time, and to some extent the weapon is more fragile and heavier, but black powder guns, bows and crossbows have their own issues. Anyone who is going to use a firearm or ranged weapon must learn how to use and maintain it, no matter what type of firearm or ranged weapon it is. A water wheel driven air compressor solves air tank filling for use here on the islands, and hand pumping will be for field use only.

  With 1 or 2 extra air tanks per weapon, air rifles gives many quick shots relative to other firearms options. Something like 30 to 90 aimed shots in a short time, with very good range and accuracy. No deafening bangs. No smoke. No pyro effect that in the dark screams 'here I am' and damage the shooters night vision and of those around. No chance of starting a forest fire or setting dry ground on fire. A firearm that doesn't care if it's raining, snowing or 100% humidity, although the barrel should still be held slightly downwards. A ranged weapon that can literally be swum with without being truly affected, and no delicate ammo that needs to be kept dry. Even bows and arrows have problems with moisture and rain. The air rifles heavy bullet does not really care about strong winds except for its relatively small lateral impact on the bullet trajectory. Virtually insensitive to the angle at which the weapon is held and can also be fired sideways and upside down. Can be shaken and handled relatively violently. Can be reloaded in any position and during movement, and easy to do by feel alone. No real barrel fouling except some lead from the bullet.

  If I make a change to the planned design, then handloading improvised 'emergency ammo' such as pebbles can be used at short ranges, with leaves as padding-seal. Maybe making wooden bullets will work? I can make a small simpler aid for forming and a template, a bit like a pencil sharpener. A longer 'arrow' could also be inserted into the barrel.

  Carried with a maintenance kit and a hand pump, the air rifle is a firearm that can be used almost anywhere for years, in mountains, desert, desert island, primeval forest or swampland, firing copious amounts of shots until the weapon is worn out or breaks. No logistical requirement for black powder, cartridges, metals or the like. With all the other advantages over black powder, a bow or a crossbow, that is not bad for a military firearm or for a survival weapon.

  As promised, I sit with 'Anna' and 'Elsa' and we watch the movie 'Frozen' before going to bed. Swedish subtitles are not ideal because Iselin and Caecilia can't read it, but it makes my live interpretation a bit easier. But they really love the movie which is very fairytale-like, and they like the trolls, hate Hans, and will forever have another view of master blade smith Olafr.

  Once again, I didn't consider everything the movie shows, and even though the movie is 'set' in something like the 1800s, we see big sailing ships, with many different sail arrangements, pendulum clocks, a lighthouse and many other things, like the opening is ice carving for an ice house where they travel home under the northern lights. There was an unexpected amount of pausing and jumping back and discussions. Iselin is so easily distracted by technology and starts thinking, while Caecilia mostly wanted to continue seeing and enjoying the artwork and story telling as it is, and was a little displeased with the interruptions. But Iselin's will takes priority with both me and Caecilia, and both will be able to see the movie again in the future.