How to tune for efficiency? And how to tune for shot count? And what impact does it have on the accuracy?
I've noticed that this is being discussed in multiple topics all the time over multiple forums and platforms and thought it would be a good idea to elaborate a bit on this. Feel free to add your experiences and questions, many knowledgeable tuners around here that can help and many that want to learn
So, let's clear something up first: efficiency in terms of liters of air per shot and shot count unfortunately do not go hand in hand. Shot count is the optimization between efficiency and headroom in pressure (between reg and fill pressure) which isn't the most efficient tune. I've written something about it in a topic once which was aimed at a short barreled FX Impact, short barrels with small reservoirs really benefit from a proper tune for shot count (gained at least about 15 to 20% in shot count).
To clear another thing up: at a lot of places on the internet you will find that the most efficient tune is to look for the regulated pressure at which you can reach just about 3m/s (10 fps) above your desired speed and back it down a little bit. While this is a really easy way to find a tight ES with in most cases good accuracy if you are around the right speed it is not at all efficient in terms of air consumption per shot. So, how am I so sure about this: numbers don't lie
Recorded three different airguns on the bench: FX Dreamline in.22 with 20cm barrel, FX Impact in .22 with 40cm barrel and an FX Impact in .30 with a 60cm long barrel. Did the same years ago with the Steyr LG110 I had but don't have the numbers anymore.
The three setups:
FX Dreamline:
FX Impact in .22 with 40cm barrel
FX Impact in .30 with 60cm barrel
With these setups I did the exact same thing: had chosen a fixed velocity to tune on and search for the lowest pressure where I could reach the speed. This is the starting point of the graph. I chose to increase the pressure per 5 bar, retune to the chosen velocity and calculate the liters of air per shot and shot count at each setpoint.
With longer barrels the effect is a bit more gradual and you're already shooting more efficient compared to short barrels. With the .22 impact I should have included about 95 bar already but it's not in the graph, at that pressure I was really on the edge of making it to the desired velocity.
What do the graphs tell us? The higher the pressure the more efficient it shoots in terms of air consumption (liters of air per shot). This can be explained by the relation between pressure and force: the higher the regulator pressure, the higher the force on the projectile which allows it to accelerate faster (up to a certain degree, law of deminishing returns). The graph for shot count however tells a slightly different story, maximum shot count is achieved at a pressure around 20% higher than the minimum required pressure to reach the velocity.
FX Dreamline: 135 bar / 110 bar = +23% higher pressure -> 45 shots / 25 shots = 80% extra shots
FX Impact .22: 115 bar / 95 bar = +21% higher pressure -> 79 shots / 56 shots = 41% extra shots
FX Impact .30: 120 bar / 100 bar = +20% higher pressure -> 65 shots / 54 shots = 20% extr shots
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How to do this test yourself you may ask: Fill the gun to a fixed pressure (I used 200 bar) and leave the hose attached without depressurizing it, shoot a magazine (28 shots in this case) and see how far the pressure has dropped. Divide that pressure drop by the amount of shots and you know how much bar / shot is used. Multiply that number by the metric volume of the reservoir (0,3 liter in this case) and you know how much liters of air are consumed per shot. To calculate how many shots you have you take the fill pressure, substract the regulator pressure from the fill pressure and multiply it by the reservoir volume -> this gives you the available amount of liters of air to shoot with. Divide the amount of available liters of air by the consumption of liters per shot and you know the amount of shots you will have. In formulas:
(200 bar – end pressure) / magazine size = bar per shot
bar per shot x volume of reservoir in liters = liters per shot
(fill pressure – reg pressure) x volume of reservoir in liters = available liters of air
available liters of air / liters per shot = amount of shots
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Does this also work for other brands than FX: yes it does! Tried this on multiple airguns and always found very similar values. What I do see as a difference is that with lightweight internals like hammer, hammerspring and valve spring (FX, Steyr and many more) you wil barely get the increase in velocity at the end of the shot string like described in Bob Sterns article: link to the article. With very heavy and overdesigned internals (typical in older designs) you will see it at the end of the curve.
What is the impact on accuracy: the 20% increase in pressure might not be the optimal for your precision node with the smallest groups but if you look at the graphs you have at least a 5 to 10 bar window around the peak point to find a node. I have always been able to find a node within this 10 bar which gave me the precision I was looking for (which of course is the best achievable precision
).
Feel free to jump in
Tom - @longrange_airgunning
I've noticed that this is being discussed in multiple topics all the time over multiple forums and platforms and thought it would be a good idea to elaborate a bit on this. Feel free to add your experiences and questions, many knowledgeable tuners around here that can help and many that want to learn
So, let's clear something up first: efficiency in terms of liters of air per shot and shot count unfortunately do not go hand in hand. Shot count is the optimization between efficiency and headroom in pressure (between reg and fill pressure) which isn't the most efficient tune. I've written something about it in a topic once which was aimed at a short barreled FX Impact, short barrels with small reservoirs really benefit from a proper tune for shot count (gained at least about 15 to 20% in shot count).
To clear another thing up: at a lot of places on the internet you will find that the most efficient tune is to look for the regulated pressure at which you can reach just about 3m/s (10 fps) above your desired speed and back it down a little bit. While this is a really easy way to find a tight ES with in most cases good accuracy if you are around the right speed it is not at all efficient in terms of air consumption per shot. So, how am I so sure about this: numbers don't lie
Recorded three different airguns on the bench: FX Dreamline in.22 with 20cm barrel, FX Impact in .22 with 40cm barrel and an FX Impact in .30 with a 60cm long barrel. Did the same years ago with the Steyr LG110 I had but don't have the numbers anymore.
The three setups:
FX Dreamline:
FX Impact in .22 with 40cm barrel
FX Impact in .30 with 60cm barrel
With these setups I did the exact same thing: had chosen a fixed velocity to tune on and search for the lowest pressure where I could reach the speed. This is the starting point of the graph. I chose to increase the pressure per 5 bar, retune to the chosen velocity and calculate the liters of air per shot and shot count at each setpoint.
With longer barrels the effect is a bit more gradual and you're already shooting more efficient compared to short barrels. With the .22 impact I should have included about 95 bar already but it's not in the graph, at that pressure I was really on the edge of making it to the desired velocity.
What do the graphs tell us? The higher the pressure the more efficient it shoots in terms of air consumption (liters of air per shot). This can be explained by the relation between pressure and force: the higher the regulator pressure, the higher the force on the projectile which allows it to accelerate faster (up to a certain degree, law of deminishing returns). The graph for shot count however tells a slightly different story, maximum shot count is achieved at a pressure around 20% higher than the minimum required pressure to reach the velocity.
FX Dreamline: 135 bar / 110 bar = +23% higher pressure -> 45 shots / 25 shots = 80% extra shots
FX Impact .22: 115 bar / 95 bar = +21% higher pressure -> 79 shots / 56 shots = 41% extra shots
FX Impact .30: 120 bar / 100 bar = +20% higher pressure -> 65 shots / 54 shots = 20% extr shots
-----------------------------------------------------------------------------------------------------------------------------------------
How to do this test yourself you may ask: Fill the gun to a fixed pressure (I used 200 bar) and leave the hose attached without depressurizing it, shoot a magazine (28 shots in this case) and see how far the pressure has dropped. Divide that pressure drop by the amount of shots and you know how much bar / shot is used. Multiply that number by the metric volume of the reservoir (0,3 liter in this case) and you know how much liters of air are consumed per shot. To calculate how many shots you have you take the fill pressure, substract the regulator pressure from the fill pressure and multiply it by the reservoir volume -> this gives you the available amount of liters of air to shoot with. Divide the amount of available liters of air by the consumption of liters per shot and you know the amount of shots you will have. In formulas:
(200 bar – end pressure) / magazine size = bar per shot
bar per shot x volume of reservoir in liters = liters per shot
(fill pressure – reg pressure) x volume of reservoir in liters = available liters of air
available liters of air / liters per shot = amount of shots
---------------------------------------------------------------------------------------------------------------------------------------------
Does this also work for other brands than FX: yes it does! Tried this on multiple airguns and always found very similar values. What I do see as a difference is that with lightweight internals like hammer, hammerspring and valve spring (FX, Steyr and many more) you wil barely get the increase in velocity at the end of the shot string like described in Bob Sterns article: link to the article. With very heavy and overdesigned internals (typical in older designs) you will see it at the end of the curve.
What is the impact on accuracy: the 20% increase in pressure might not be the optimal for your precision node with the smallest groups but if you look at the graphs you have at least a 5 to 10 bar window around the peak point to find a node. I have always been able to find a node within this 10 bar which gave me the precision I was looking for (which of course is the best achievable precision
).Feel free to jump in
Tom - @longrange_airgunning
Yes it's pretty aligned, using a higher pressure is more efficient and you can turn down the speed with the hammer spring adjuster.