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      by Published on 19-07-2017 19:20 PM
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      In my experience air cylinders for filling PCPs are one of the least-understood areas of airgunning; an issue compounded ...
      by Published on 13-03-2013 21:57 PM  Number of Views: 5211 

      I thought I would take the time to explain the differences between a spring and a Gas Ram/Strut as there is a bit of confusion and misunderstanding of the differences of operation between the two. I make no claim to be an expert on either springs or physics. (Mods, you might want to make this a ‘Sticky’)

      So, first of, lets look at the two items in question.

      Spring.



      A Spring Airgun is powered by a coil spring that has evenly spaced coils known as a ‘Linear rate’ spring. The spring is manufactured by winding round section (or sometime square section) spring steel in a coil to give the classic spring shape. The spring works by placing the steel in torsion when it is compressed. That is to say, the steel is actually twisted every slightly along it’s length when compressed. The spring steel wants to always resist this torsional twisting and this is what makes the spring to return to its untwisted state and in doing so, provides the force that acts against compression.

      So, if you paid attention in your physics class at school (who didn’t? own up) you may remember something called ‘Hookes Law’. Basically this chap called Hooke came up with a simple formula that states if a spring is deflected (compressed or stretched) by a force X and compresses/extends by a factor of Y, then for a compression force of 2X the spring will deflect by a factor of 2Y. Put in simple terms, if 1kg of force compresses the spring by 1cm, then 2kg will deflect the spring by 2cm. 8 kg will deflect the spring by 8cm etc etc. There will come a point when the force applied to the spring will cause the spring to fail, this is known as exceeding Hookes law. Have you ever held a small extension spring from a ballpoint pen and stretched it and noticed there comes a point when the spring no longer keeps its shape? in this case the force you applied has exceeded Hookes law.

      Hookes law explained;





      Key Point –

      The fact that with a spring, if you double the force, you double the amount of stretch/compression of the spring. If a spring is compressed with a force of 10kg and the spring is then restrained (held back) it has the force of 10kg (latent energy) wanting to extend it back to its natural uncompressed/stretched state. In a cocked spring air rifle, the force used to compress the spring is the same force that wants to extend the spring and push the piston forward. When fired, at the halway point of the pistons travel the force acting on it is also halved.

      Gas Ram/Strut



      In a gas ram, there is sealed cylinder within which is a sealed piston attached to a compression rod. In front of the piston is a gas (air in most cases). When the compression rod is pushed into the cylinder, the piston is moved forward and compresses the air in front of it. Gases or in this case air, don’t like being compressed and instead want to return to their pre-compressed state which in most cases is atmospheric pressure.

      So, if after paying attention in your physics class you remembered Hookes law, you may have stayed awake long enough to remember Boyles law. Now this chap Boyle was interested in Gases and what happens when you compress them. He came up with another simple formula that states that the absolute pressure and volume of a given mass of confined gas are inversely proportional, if the temperature remains unchanged within a closed system. In other words, when the volume is halved, the pressure is doubled; so if the volume is doubled, the pressure is halved. So in our Gas Ram, if we compress the volume of gas inside it by halving it (by pushing the piston against it) the pressure of the gas is doubled. All very good, so know if we halve the volume again with more compression, that pressure is again doubled to what it was. In other words, unlike a linear spring rate where everything is double X = double Y, in a Gas Ram, the compression rate is not Linear but progressive. With each bit of compression movement, we need a lot more force to overcome the pressure of the gas. People often notice that an Air rifle with a Gas Strut is harder to cock at the end of the stroke because the force acting against the piston is becoming greater and greater but disproportionate to the amount of force on the cocking lever. This is Boyles law in action.

      Boyles law explained and demo;

      http://en.wikipedia.org/wiki/File:Bo...w_animated.gif



      Key Point –

      With a Gas Strut in its compressed state, the initial force acting against the piston will diminish faster as the gas is allowed to expand against the piston and the relationship of this force to the pistons movement is NOT LINEAR. If a Gas Strut is compressed with a force of 10kg and the piston rod is then restrained (held back) it has the force of 10kg (latent energy) wanting to extend it back to its natural uncompressed/stretched state. But by halfway through it extension, the force is not 5KG but proportionately less.

      What does this mean in terms of the difference in ‘lock time’ between the two?

      By the term ‘Lock Time’ we are referring to what happens when we pull the trigger and the energy stored within either the spring or Gas Strut is released.

      Spring gun

      By remembering our key point, in the spring gun the piston is forced forward with a progressively diminishing force exerted by the spring. Without getting into the physics of acceleration and in order to keep it simple, when the trigger releases the sear the piston is pushed forward with a relatively smooth acceleration force along it length of travel. As we know, every force has an equal and opposite force and in this case, this produces the familiar backwards nudge of the gun we call ‘Recoil.

      Gas Ram

      Again, by remembering our key point that the compression of the strut is not linear, when the trigger releases the sear, a greater amount of force than in a spring gun (due to the compressed Gas) pushed the piston forward very rapidly but this force rapidly diminishes along the pistons travel, however the force exerted in the initial phase of the acceleration more than makes up for the rapidly diminishing force as the piston moves forwards. Again, we know that for each force there is an equal and opposite force and in the case of the Gas Ram, the force is rapid recoil that is over very quickly.

      To put the comparison between the two into layman’s terms, imagine two cars, one powered by a large petrol engine, the other by a short burn but powerful rocket. The petrol car will accelerate rapidly but progressively (spring gun) and the rocket car with shoot forwards more rapidly but runs out of puff shortly after. In an air rifle, it is this initial acceleration that is the part that we are interested in.

      What does all this mean in terms of shooting a Spring Gun or a Gas Ram?

      Gas Rams are a bit like Marmite, you either love them (many do) or some people just don’t get on with them. In terms of shooting, with a Gas Ram the initial recoil kick is much sharper but lasts less time, whereas in a spring gun the recoil is smoother but over a longer period. There are many arguments for accuracy with both spring and Gas Strut but it may be that the shorter ‘snappier’ recoil of a Gas Ram may upset the aim less as it is over and done with so quickly whereas with a spring gun, the shooter must ‘follow through’ with the shot for longer.

      Q&A’s

      1. Q -Will a Gas Ram make my spring gun a PCP?
      A – No it won’t. It is a Gas Strut Air Rifle

      2. Q – Can I fit a Gas Ram conversion to any spring gun?
      A – Not all air rifles. Due to the design of a Gas Strut, they can only be fitted into Spring Guns that DO NOT have a rod running through the centre of the piston for the trigger sear to engage (as per HW’s and Air Arms & Others)

      3. Q – Will a Gas Strut make my rifle quieter internally?
      A – Yes it should, as there is only the strut and the piston without any spring or guides to rattle around inside the rifle when firing

      4. Q – Will a Gas Strut improve my air rifle?
      A – in many cases YES, however they are like Marmite and not all guns seem to suit a Gas Ram conversion

      5. Q - Will a Gas Ram keep is ‘power’?
      A – In theory, if it doesn’t leak any gas it will last indefinitely at the same power, however they do tend to lose a bit of gas over time

      6. Q – Are Gas Rams better suited to FAC levels?
      A – Gas rams can be used at below and above FAC levels but for VERY high power FAC levels it can be argued that a Gas Rams is better suited than a spring.

      7. Q - Can I leave a Gas Ram cocked indefinitely?
      A - As long as no gas (air) leaks out, a compressed gas strut will retain its extension force indefinitely but in reality, a certain amount of gas leakage over time is to be expected.

      8. Q - Are Springs or Gas Rams affected by temperature?
      A - A spring on it's own won't be affected by normal ranges of temperature it will encounter in use, however, the grease that is lubricating it will, becoming more viscous in the cold and less viscous with heat, both of which will have an affect on it's operation. In theory, a Gas Ram WILL be affected by temperature since it contains sealed gas and with a rise in temperature, the gas will want to expand and in theory exert more force. However, I have yet to see any evidence to back this up to date.

      Lastly

      I make no claims to be an expert on either Gas Rams, Springs or Physics. If anyone feels that any element of this post needs correcting then please PM me, let me know the problem and if required, I will amend the post accordingly.

      Hope you enjoy the read and find it interesting.
      by Published on 18-12-2012 17:43 PM  Number of Views: 6201 

      The Scottish Government has announced that it will introduce a law requiring that all low powered airguns be registered. It hasstated that it will not consult on whether or not to introduce this law, only on how it will be introduced.
      The only way forward at this stage to help prevent this draconian piece of legislation being enacted is for all shooting disciplines from throughout the UK and right thinking people to come together and express their feelings. If it is not stopped, further restrictions will follow.
      The “proposals” can be read through this link, worth doing to see how ill thought out and undemocratic they are.
      http://www.basc.org.uk/en/utilities/document-summary.cfm/docid/EDAB451D-4992-46C2-A36905E394383BB8
      The introduction of this law can be stopped but this will require action from the whole shooting community.
      Please sign, as a first step, the BASC led petition at:
      https://www.change.org/en-GB/petitions/scottish-government-to-drop-all-proposals-to-licence-air-weapons-in-scotland
      Please pass this on to your fellow shooters, friends andfamily and ask them to sign as well.
      Many thanks
      by Published on 17-07-2012 07:32 AM  Number of Views: 35666 

      Well thanks to some of you guys helping with testing, Chrono Connect Mobile is now available on Google Play!

      It comes in 2 flavours, Lite and Pro.

      Lite

      The Lite version has all the basic functionality you need to read the speed of a shot from your gun. You need to enter 3 distances, the pellet weight and the pellet BC value ( Most available at ChronoConnect.com ) and you can begin shooting.



      The app will display the speed of the pellets, the power it equates to and the min and max values recorded for each.

      Pro

      The Pro version has many more cool features such as,


      • Unlimited shots in one go ( no 3 shot 'Lite' limit ).
      • Full list of shots in the string.
      • Graph of shots in the string.
      • Full shot and string management.
      • Comprehensive pellet database ( no need to manually enter weights and BC values for most pellets )
      • Comprehensive rifle and pistol database.
      • Visual over power warnings.




      Both are available now on Google Play. Lite is FREEEEE so why not download it and have a play.

      Cheers
      Stot
      by Published on 24-05-2012 23:49 PM  Number of Views: 11858 

      Well we will have stocks of these very soon three types

      Synthetic LGV Challenger Ultra will be £374.95 approx

      Wooden LGV Master Ultra will be £449.95

      Wooden LGV Competition Ultra Field Target will be £490

      Here's what all the fuss is about!









      by Published on 14-12-2011 21:25 PM  Number of Views: 9434 

      The subject of V Mach kits crops up a lot in terms of where do I get one, what do they do, how easy are they to fit etc so I have started to produce a V Mach 'guide', having fitted a fair few myself over the years. Perhaps we can make this a 'Sticky' on the forum. Please feel free to add anything and if suitable, I can add this into the guide.


      1. What is a V Mach ‘Tuning’ Kit?

      A V Mach kit is a kit of precision custom internal components, tailored for each individual air gun that replaces the standard factory fitted internal components. V Mach kits vary from model to model of air gun but some may contain additional components to those fitted as standard by the factory. All Kits come with components, Lubricants and a set of fitting instructions.

      Here is a typical V Mach Kit contents




      2. Where do you get a V Mach kit from?

      V Mach Kits can be supplied direct form V Mach
      http://www.air-rifle-tuning.com/v-mach/Home.html.
      Alternatively you can purchase them from Blackpool Air Rifles
      http://airgunbuyer.com/
      or DAI Leisure
      http://www.daileisure.co.uk/

      There are other suppliers but these are the main 3. Note:, if buying direct from V Mach, the owner Steve Pope is incredibly helpful and will provide phone/email support if required but please bare in mind he is a very busy man.

      There are also various air rifle tuners around the country who will supply and fit a V Mach kit for you. Top tuner Lyn Lewington is able to supply and fit a V Mach Kit for you – Tel 07530 381169 email airrifletuner@hotmail.com

      3. How easy is a V Mach Kit to fit?

      For the most part, a V Mach kit is able to be fitted by anyone with a basic set of tools and a modicum of knowledge. Difficulty will vary from airgun to airgun but if you have ever stripped and rebuilt your airgun you are capable of fitting a V Mach Kit. CAUTION – On some airguns the factory spring may be under a lot of pre-load and some form of spring compressor may be required for safety reasons. When fitting a V Mach kit, it is often the case that the V Mach spring is under LESS pre-load than the factory spring and therefore reassembly is much easier. The current UK power limit for non FAC airguns is 12 f/lbs and therefore it is ESSENTIAL that after fitting a V Mach kit the power is checked using a Chronograph to ensure the airgun remains under 12 f/lbs. It is a criminal offence to possess a FAC airgun without an Fire Arms liscence!!

      Here are the fitting instructions for a typical Airgun (Weihrauch HW80)
      https://files.me.com/v_mach/cu1zs9


      4. What difference will a V Mach kit make to your airgun?

      The V Mach kit is designed to Smooth the firing cycle of the airgun. It is NOT designed to make it more powerful although fine tuning of the final power level is possible by adjusting the spring preload using washers supplied in the kit (See note above re UK law for airgun power levels.

      The Main benefits are;
      · Less spring noise during firing, often referred to as ‘Twang’
      · Less recoil during firing
      · More consistent power levels shot to shot
      · Increased accuracy due to less recoil
      · Easier to cock
      · Restoration of factory power levels (and in some cases an increase) in worn airguns
      . Increase in re sale value of the gun due to incresed desireability

      5. What are the Nylon Spring Guide and 'Top Hat' for?

      Most airguns come as standard with a metal spring guide. As the spring uncoils from this during firing,the metal to metal contact can result in 'spring twang' as it is metal to metal contact. The Nylon spring guide within the kit smooths the process of the spring extending and prevent metal to metal contact, reducing spring 'twang'. The 'top hat' fits inside the piston and again, prevents metal to metal contact and when the rifle is cocked, the top hat and guide almost meet, meaning the spring is secured in perfect alignment on a continuous tube and when fired, the spring is able to extend smoothly, progressively and under control, reducing recoil and noise.

      6. How much grease should I use?

      As per the instructions, only use the supplied Moly Grease (NOT the supplied oil) to lubricate the piston seal, spring guide, top hat and piston skirt. A thin smear is all that is required, taking care not to get any on the face of the piston seal. Take care not to overdo the amount of grease.

      7. Why is the spring covered in a sticky white grease?

      This extra thick adhesive grease is designed to slow down the rate that the spring extends from the spring guide when firing by providing a level of adhesion between the spring and guide. This adhesion reduces the recoil on firing as the spring is extending gradually rather than being released in an uncontrolled manner.

      8. What power level should I aim to get?

      The UK legal limit is 12 F/Lbs for airguns (Rifles) and therefore a sensible 'buffer' is required to ensure your airgun stays within the legal limit. As a general guide, DO NOT exceed 11.5 F/Lbs after assembly. IMPORTANT Once the V Mach Kit is fitted, the components, especially the seal will 'bed in' and the power will increase. It is wise to re check the power level after 500 pellets to ensure the airgun power has not crept above 12 F/Lbs. Power levels are altered by adding/subtracting the supplied washers that fit inside the piston between the top hat and piston crown.

      9. I can't cock my airgun after fitting my V Mach Kit?

      If too many spring preload (power adjusting ) washers are added, it is possible in some rifles that the spring bcomes 'coil bound' (coils touch and cannot compress any further). If this happens, the piston will not be allowed to travel backwards far enough to engage the sear/safety. De-Cock the gun and remove a washer and try again.
      by Published on 10-08-2011 18:37 PM  Number of Views: 6308 

      Version 1.6 is out already.



      It now has some online functionality allowing you to submit guns and pellets to the database from inside the program and also allow you to update your own copy of the program to match the online databases whenever you like.


      Also unlocking can be done in program now making it much easier, and ProChrono Digital can now dump down its any of its saved strings into the program. Cheers to Andy for helping me get that right.

      www.chronoconnect.com

      Cheers
      Stot

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