Technical Info from FAS part 5
Page 1 of 1
Technical Info from FAS part 5
kuya jhas Fri Aug 29, 2008 3:22 am
Long barrels need Boreup Kits:
Since wolv didnt run over bore up cylinders.... bore up cylinders have a thinner cylinder wall as well as a larger bore on the cylinder head nozzle. Due to this larger bore the nozzle must be a larger bore. This basically gets you a minimal increase in volume throughout the whole system. It has the downside of each part being unique and non replaceable for the most part. Going to wolv's explanation I have seen several boreup kits that resulted in a drop of BB velocity. Not what someone wants after spending 50 to 100 bucks on an upgrade. This is due to their being a larger volume of air that the same sized spring is trying to push. So if your gun was shooting 400 with and you put in the boreup kit because you bought into the marketing hype you would probably end up shooting around 385 after. In my opinion they are a waste of money. To prove this I built a g36 up with a RAS and a 650 mm PSG barrel....longest barrel available on the market. I have an M120 and type 0 cylinder installed and the gun shoots consistantly 400 to 405.
You need a long barrel for range/fps/whatever. Barrels give you accuracy and can contribute to range due to the volume that they possess. I constantly hear about everyone wanting to make their barrel longer to get better range or more FPS. As you have seen it is a science. You need to have a barrel that matches the volume of air that your cylinder is pushing out. Your velocity is coming from the compression of the air from your spring. As wolv said if your barrel contains less volume than your cylinder you are wasting some of that compression your spring generates. My G3SAS has one of the shortest barrels out there. It actually has the stock cylinder in it which has a hole in it. With an M120 the gun will only shoot around 350fps. This is because the gun has half the barrel/cylinder volume of an SR16 for example. To compensate for this I put an M130 into the gun. This has the effect of compressing the air faster to generate more pressure. This gets the bb up to speed before it leaves the barrel. This results in it shooting 400 fps. Now lets look at the flip side....Longer barrels. In my opinion the G3 has the perfect length barrel. I have g3 barrels in my P90, SR47, the other G36 and a couple other guns. When you pull the trigger and the piston slams forward compressing that air you get a very violent turbulent reaction. All of this compressed air blasts out and hits the bb pushing it past the hopup which starts it spinning. Some distance down the barrel after that the bb is going to be moving at its terminal velocity. The advantage of a longer barrel or a tightbore barrel is that it holds the BB in that trajectory for a longer time. Basically it removes some of the erratic behavior of the bb. To test that compare a g3 to a Mp5k. The K will spray BBs everywhere wheres the G3 puts out a beam of bbs.
From what I have seen the single greatest effect on the FPS of your gun is the level of your technical expertise. You can take the best parts in the world, slap them together and still have a gun shooting stock velocities. You can also take a new M120 and get a gun shooting consistantly 410 to 420.
What's better, a long barrel or a short one? For the most part a longer barrel works better than a shorter one. Why? Well aside from the obvious explanation that a longer barrel will be more accurate many people don't realize it'll also give you more power and velocity. When the air is compressed in the cylinder it creates pressure which leads to force. Pressure, P, is the force acted on an object, F, per unit area, a.
P = F / a
Force equals mass times acceleration, F = MA. The mass of the BB doesn't change as it travels, so all of the force goes towards acceleration. All objects move in a constant speed (even if that speed is zero) in a single direction unless force is exerted on the object. When force is exerted the speed or velocity will change, meaning there is acceleration. Acceleration is the change in velocity over time. If a car goes 30mph on the street and speeds up to 35mph in 5 seconds, then 40mph in 10 seconds, it is accelerating by 1mph per second. When acceleration stops, that does not mean the object stops moving. In the case of the car, it remains at the final constant speed of 40mph.
So pressure results in the acceleration of an object. This acceleration is proportional to the cross sectional area of the object, and inversely proportional to the mass of the object.
P = MA / a
Ok what's that have to do with barrel length? The more time a force is exerted on an object the longer it will be accelerated, and the more it accelerates the faster it will go in the end. Obviously a BB will take longer to travel down a long barrel than a short one, thus it will have air pressure exerted on the BB for a longer amount of time and that means more time to accelerate. This is why you will get more velocity from a long barrel than a short one. Example: a SP110 spring in a M4A1 will give a velocity near 390fps (depending on what other parts are installed), but that same spring in a MP5K will only give 300fps.
HOWEVER, electric powered airsoft guns get their pressure and force only from the air being compressed in the cylinder. It is a specific volume of air that once compressed will want to return to its original volume. Therefore, if the volume of the barrel is larger than the volume of the cylinder than you will get a suction effect in the barrel. Let's say your piston and cylinder will push out 40 cubic centimeters of air and your barrel volume is 60 cubic centimeters. Your piston only has enough air to push the BB two-thirds way down the barrel. Two-thirds way down your BB will reach its maximum velocity and will travel on inertia alone. But in that last third the BB will act like a piston in reverse as it goes down the barrel and cause suction behind it. This suction will want to pull the BB back to its optimal position, two-thirds way down the barrel. Fortunately the BB will have enough inertia to still shoot out, however it will have a lower than optimal velocity because of the suction caused in the barrel will pull it back. In this respect a barrel that is too long will not be good. As an example the HammerMods.Com crew and I experimented with putting a PSG-1 barrel in a M16A2. The A2 was upgraded to shoot 400fps with the A2 length barrel. But with the PSG-1 barrel it shot only slightly over 320fps. Obviously the PSG-1 barrel was too long for the A2 piston and cylinder. Just as a side note the M16A2 has a full, non-ported cylinder, meaning it pushes out the maximum amount of air for version 2 mechboxes.
What does that last statement mean? The cylinders in many of the AEG's have holes in them. This is to port out air. Why do you want air ported out? Well, the concept of force being exerted for a longer time leading to more acceleration is at work here, too. The spring in the mechbox exerts force on the piston making it accelerate. This means that the piston is moving slow in the beginning of the piston stroke and fast at the end. Let's say the barrel has a volume of 20 cubic centimeters. If the cylinder contains 40 cubic centimeters of air you only need to use half of the air inside. To get the optimum performance you want the fastest moving portion of the air, the second half (remember, the air accelerated at the end of the stroke will be moving faster). The first half of the air being compressed is unnecessary because it is moving too slow and will push out the BB before the faster portion of air will even touch the BB. So to get rid of the first half a hole is made in the cylinder to let the air out before it is compressed.
The cylinders in many of the AEG's have holes in them. My friend and customer experienced this problem when his friend installed an AK-47 full tune up kit in his AK-47B Spetsnaz. This included an AK-47 bore-up cylinder and piston head. He gained a substantial increase in velocity but when he finally checked it on a chronograph it showed lower than expected readings. He told me about what was done to his gun and I advised him to switch his bore-up cylinder to a ported MP5 standard bore cylinder (with matching heads and nozzle). He took my advice and we switched the parts out. This change alone resulted in a 20-25fps increase without changing the spring.
So if you want the most velocity for your parts you should use a long barrel. However, if you do not have a cylinder that matches your barrel you will be losing velocity. So before you put a AK-47 barrel on your MP5, or a SG-1 bore-up cylinder in your G3 SAS, stop and think about what you need to do and how it will affect your performance.
Bore up and Silent Piston Head's SUCK!
I'm not saying that the idea of larger bore being beneficial is wrong, but the shapes of the piston heads are all wrong. The convex head leads to turbulence and lower fluid flow rates. This is why:
Friction is everywhere. Even air has friction. Friction leads to deceleration in moving objects. As air moves down a tube the air molecules have friction against the sides of the tube. This slows the air near the walls of the tube while the air in the center moves faster. This in itself results in a convex flow of air as it travels down a tube.
This causes turbulence because air molecules will feel faster flow near the center of the tube and slower flow on the outer perimeter. When you have an object moving at a faster speed on one side than the other you will experience rotation. This is like how tanks steer, by moving one track faster than the other the tank turns. And when objects spin they want to change their trajectory. Imagine your gun with too much hop-up. The bb's are spinning too fast and end up curving rather than shooting straight. This is exactly what happens to the air molecules; they curve out towards the walls of the tube instead of moving straight down the tube.
The amount of curve in the convex shape of the airflow determines the amount of turbulence. This is because the difference in airflow velocities on opposite sides of the air molecules is greater. The greater difference causes more spin. Using a convex piston head increases this curve and causes more turbulence. This results in inefficient airflow.
Why do they make convex piston heads? Well because tapered cylinder heads help reduce turbulence and [dumb] people feel believe that the curved piston head will help use all of the air in the cylinder instead of leaving a small portion of unused air in the cylinder head. If [dumb] people don't believe what I explained about turbulent flow then maybe they'll believe that you'll have more air volume with a flat piston head (which you do but that is unusable tidal air volume that won't do anything). But who knows, people believe anything they read on the internet no matter how dumb it may be.
Since wolv didnt run over bore up cylinders.... bore up cylinders have a thinner cylinder wall as well as a larger bore on the cylinder head nozzle. Due to this larger bore the nozzle must be a larger bore. This basically gets you a minimal increase in volume throughout the whole system. It has the downside of each part being unique and non replaceable for the most part. Going to wolv's explanation I have seen several boreup kits that resulted in a drop of BB velocity. Not what someone wants after spending 50 to 100 bucks on an upgrade. This is due to their being a larger volume of air that the same sized spring is trying to push. So if your gun was shooting 400 with and you put in the boreup kit because you bought into the marketing hype you would probably end up shooting around 385 after. In my opinion they are a waste of money. To prove this I built a g36 up with a RAS and a 650 mm PSG barrel....longest barrel available on the market. I have an M120 and type 0 cylinder installed and the gun shoots consistantly 400 to 405.
You need a long barrel for range/fps/whatever. Barrels give you accuracy and can contribute to range due to the volume that they possess. I constantly hear about everyone wanting to make their barrel longer to get better range or more FPS. As you have seen it is a science. You need to have a barrel that matches the volume of air that your cylinder is pushing out. Your velocity is coming from the compression of the air from your spring. As wolv said if your barrel contains less volume than your cylinder you are wasting some of that compression your spring generates. My G3SAS has one of the shortest barrels out there. It actually has the stock cylinder in it which has a hole in it. With an M120 the gun will only shoot around 350fps. This is because the gun has half the barrel/cylinder volume of an SR16 for example. To compensate for this I put an M130 into the gun. This has the effect of compressing the air faster to generate more pressure. This gets the bb up to speed before it leaves the barrel. This results in it shooting 400 fps. Now lets look at the flip side....Longer barrels. In my opinion the G3 has the perfect length barrel. I have g3 barrels in my P90, SR47, the other G36 and a couple other guns. When you pull the trigger and the piston slams forward compressing that air you get a very violent turbulent reaction. All of this compressed air blasts out and hits the bb pushing it past the hopup which starts it spinning. Some distance down the barrel after that the bb is going to be moving at its terminal velocity. The advantage of a longer barrel or a tightbore barrel is that it holds the BB in that trajectory for a longer time. Basically it removes some of the erratic behavior of the bb. To test that compare a g3 to a Mp5k. The K will spray BBs everywhere wheres the G3 puts out a beam of bbs.
From what I have seen the single greatest effect on the FPS of your gun is the level of your technical expertise. You can take the best parts in the world, slap them together and still have a gun shooting stock velocities. You can also take a new M120 and get a gun shooting consistantly 410 to 420.
What's better, a long barrel or a short one? For the most part a longer barrel works better than a shorter one. Why? Well aside from the obvious explanation that a longer barrel will be more accurate many people don't realize it'll also give you more power and velocity. When the air is compressed in the cylinder it creates pressure which leads to force. Pressure, P, is the force acted on an object, F, per unit area, a.
P = F / a
Force equals mass times acceleration, F = MA. The mass of the BB doesn't change as it travels, so all of the force goes towards acceleration. All objects move in a constant speed (even if that speed is zero) in a single direction unless force is exerted on the object. When force is exerted the speed or velocity will change, meaning there is acceleration. Acceleration is the change in velocity over time. If a car goes 30mph on the street and speeds up to 35mph in 5 seconds, then 40mph in 10 seconds, it is accelerating by 1mph per second. When acceleration stops, that does not mean the object stops moving. In the case of the car, it remains at the final constant speed of 40mph.
So pressure results in the acceleration of an object. This acceleration is proportional to the cross sectional area of the object, and inversely proportional to the mass of the object.
P = MA / a
Ok what's that have to do with barrel length? The more time a force is exerted on an object the longer it will be accelerated, and the more it accelerates the faster it will go in the end. Obviously a BB will take longer to travel down a long barrel than a short one, thus it will have air pressure exerted on the BB for a longer amount of time and that means more time to accelerate. This is why you will get more velocity from a long barrel than a short one. Example: a SP110 spring in a M4A1 will give a velocity near 390fps (depending on what other parts are installed), but that same spring in a MP5K will only give 300fps.
HOWEVER, electric powered airsoft guns get their pressure and force only from the air being compressed in the cylinder. It is a specific volume of air that once compressed will want to return to its original volume. Therefore, if the volume of the barrel is larger than the volume of the cylinder than you will get a suction effect in the barrel. Let's say your piston and cylinder will push out 40 cubic centimeters of air and your barrel volume is 60 cubic centimeters. Your piston only has enough air to push the BB two-thirds way down the barrel. Two-thirds way down your BB will reach its maximum velocity and will travel on inertia alone. But in that last third the BB will act like a piston in reverse as it goes down the barrel and cause suction behind it. This suction will want to pull the BB back to its optimal position, two-thirds way down the barrel. Fortunately the BB will have enough inertia to still shoot out, however it will have a lower than optimal velocity because of the suction caused in the barrel will pull it back. In this respect a barrel that is too long will not be good. As an example the HammerMods.Com crew and I experimented with putting a PSG-1 barrel in a M16A2. The A2 was upgraded to shoot 400fps with the A2 length barrel. But with the PSG-1 barrel it shot only slightly over 320fps. Obviously the PSG-1 barrel was too long for the A2 piston and cylinder. Just as a side note the M16A2 has a full, non-ported cylinder, meaning it pushes out the maximum amount of air for version 2 mechboxes.
What does that last statement mean? The cylinders in many of the AEG's have holes in them. This is to port out air. Why do you want air ported out? Well, the concept of force being exerted for a longer time leading to more acceleration is at work here, too. The spring in the mechbox exerts force on the piston making it accelerate. This means that the piston is moving slow in the beginning of the piston stroke and fast at the end. Let's say the barrel has a volume of 20 cubic centimeters. If the cylinder contains 40 cubic centimeters of air you only need to use half of the air inside. To get the optimum performance you want the fastest moving portion of the air, the second half (remember, the air accelerated at the end of the stroke will be moving faster). The first half of the air being compressed is unnecessary because it is moving too slow and will push out the BB before the faster portion of air will even touch the BB. So to get rid of the first half a hole is made in the cylinder to let the air out before it is compressed.
The cylinders in many of the AEG's have holes in them. My friend and customer experienced this problem when his friend installed an AK-47 full tune up kit in his AK-47B Spetsnaz. This included an AK-47 bore-up cylinder and piston head. He gained a substantial increase in velocity but when he finally checked it on a chronograph it showed lower than expected readings. He told me about what was done to his gun and I advised him to switch his bore-up cylinder to a ported MP5 standard bore cylinder (with matching heads and nozzle). He took my advice and we switched the parts out. This change alone resulted in a 20-25fps increase without changing the spring.
So if you want the most velocity for your parts you should use a long barrel. However, if you do not have a cylinder that matches your barrel you will be losing velocity. So before you put a AK-47 barrel on your MP5, or a SG-1 bore-up cylinder in your G3 SAS, stop and think about what you need to do and how it will affect your performance.
Bore up and Silent Piston Head's SUCK!
I'm not saying that the idea of larger bore being beneficial is wrong, but the shapes of the piston heads are all wrong. The convex head leads to turbulence and lower fluid flow rates. This is why:
Friction is everywhere. Even air has friction. Friction leads to deceleration in moving objects. As air moves down a tube the air molecules have friction against the sides of the tube. This slows the air near the walls of the tube while the air in the center moves faster. This in itself results in a convex flow of air as it travels down a tube.
This causes turbulence because air molecules will feel faster flow near the center of the tube and slower flow on the outer perimeter. When you have an object moving at a faster speed on one side than the other you will experience rotation. This is like how tanks steer, by moving one track faster than the other the tank turns. And when objects spin they want to change their trajectory. Imagine your gun with too much hop-up. The bb's are spinning too fast and end up curving rather than shooting straight. This is exactly what happens to the air molecules; they curve out towards the walls of the tube instead of moving straight down the tube.
The amount of curve in the convex shape of the airflow determines the amount of turbulence. This is because the difference in airflow velocities on opposite sides of the air molecules is greater. The greater difference causes more spin. Using a convex piston head increases this curve and causes more turbulence. This results in inefficient airflow.
Why do they make convex piston heads? Well because tapered cylinder heads help reduce turbulence and [dumb] people feel believe that the curved piston head will help use all of the air in the cylinder instead of leaving a small portion of unused air in the cylinder head. If [dumb] people don't believe what I explained about turbulent flow then maybe they'll believe that you'll have more air volume with a flat piston head (which you do but that is unusable tidal air volume that won't do anything). But who knows, people believe anything they read on the internet no matter how dumb it may be.
kuya jhas- Posts : 15
Join date : 2008-08-29
Similar topics» Technical Info from FAS part 2
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» Technical Info from FAS part 6
» Technical Info from FAS part 7
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