Chasing my tail? No. I was simply trying to rule something out. Never having experienced clipping, I asked what I was looking for - physical marks on the moderator etc. Thank you for your very intuitive response though
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Moderator clipping question
- Thread starter Blueduck
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Never make a change to correct a fault you are not certain you have. That's what I meant about chasing your tail. The best way to rule out clipping as your cause is by using a test rod. I have said this before and I will repeat it again. Clipping is a very common issue because moderators mount on air guns via the shroud not just the barrel. The shrouds are not always square with the barrel and this is the primary reason the bore size is so much larger than necessary on commercially sold moderators.Chasing my tail? No. I was simply trying to rule something out. Never having experienced clipping, I asked what I was looking for - physical marks on the moderator etc. Thank you for your very intuitive response though
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steve-l,
Your rod method is great for verifying static alignment. When you actually shoot your airgun, additional clearance may be required to tolerate the fact that the barrel and moderator no longer form a straight line, due to barrel flex; or harmonics. if you prefer. Especially considering the typical skinny PCP barrel. The pellet will be travelling parallel to the section of barrel at the muzzle as it leaves, starting with the bore location at the pellet's release. Meanwhile the moderator may be travelling up, down or sideways, as the pellet is travelling down successive baffle bores. How much is such dynamic misalignment? More than zero.
Unless your PCP has a very stiff barrel, or is shooting at low power, perfect static alignment of the moderator bore to the barrel bore does not guarantee that every pellet will still have sufficient dynamic clearance. On top of that, the occasional pellet can wobble or yaw due to variation or imperfections in manufacture.
As you have impressed on us many times, the mods you make have perfect alignment with your airgun barrels. Such perfect alignment often does not exist when commercial airgun barrel, shrouds and moderators are combined. So, your range rod would be useful in condemning a poor combination of parts, but what is the solution in such a case? To measure and correct each aspect of each part until they have near perfect alignment. Not everyone has the tools or the skills to fix commercial airgun parts; so they instead use moderators with larger bores to provide more margin against clipping.
Your insistence that moderators have tight baffle bores because anything less makes them less effective, is like telling all vehicle owners to take their vehicles to a calibrated engine dynamometer shop, and to pay to have their engines "blue-printed", should they fall short of the best power and torque such engines are known to produce. This despite the fact that the vehicle owner had been perfectly happy with the on-road performance of the vehicle, as measured by their butts. In like manner, the majority of airgunners are happy with the sound reduction of their factory made moderators, despite the fact that it may be possible to improve that by 2 dB by fixing the "sloppy manufacturing" of commercial airguns parts and accessories.
Your model is like tuning drag racing car to produce the very shortest quarter miles time, to brag about it, just before the engine blows up and has to be rebuilt. Many people have simpler needs when it comes to the mods they attach to their airguns. They trust their ears; rather than buying and using expensive calibrated dB meters, in a controlled and approved lab setting, just so they can convince themselves or others that the mod they are using is the best, to the nearest dB. Often in engineering and commerce, the pursuit of perfection is the enemy of good. Settling for good enough or better than expected is not a mortal sin. Despite falling short of the very best possible with a given set of parts. All of whom have been remade to perfection.
Your rod method is great for verifying static alignment. When you actually shoot your airgun, additional clearance may be required to tolerate the fact that the barrel and moderator no longer form a straight line, due to barrel flex; or harmonics. if you prefer. Especially considering the typical skinny PCP barrel. The pellet will be travelling parallel to the section of barrel at the muzzle as it leaves, starting with the bore location at the pellet's release. Meanwhile the moderator may be travelling up, down or sideways, as the pellet is travelling down successive baffle bores. How much is such dynamic misalignment? More than zero.
Unless your PCP has a very stiff barrel, or is shooting at low power, perfect static alignment of the moderator bore to the barrel bore does not guarantee that every pellet will still have sufficient dynamic clearance. On top of that, the occasional pellet can wobble or yaw due to variation or imperfections in manufacture.
As you have impressed on us many times, the mods you make have perfect alignment with your airgun barrels. Such perfect alignment often does not exist when commercial airgun barrel, shrouds and moderators are combined. So, your range rod would be useful in condemning a poor combination of parts, but what is the solution in such a case? To measure and correct each aspect of each part until they have near perfect alignment. Not everyone has the tools or the skills to fix commercial airgun parts; so they instead use moderators with larger bores to provide more margin against clipping.
Your insistence that moderators have tight baffle bores because anything less makes them less effective, is like telling all vehicle owners to take their vehicles to a calibrated engine dynamometer shop, and to pay to have their engines "blue-printed", should they fall short of the best power and torque such engines are known to produce. This despite the fact that the vehicle owner had been perfectly happy with the on-road performance of the vehicle, as measured by their butts. In like manner, the majority of airgunners are happy with the sound reduction of their factory made moderators, despite the fact that it may be possible to improve that by 2 dB by fixing the "sloppy manufacturing" of commercial airguns parts and accessories.
Your model is like tuning drag racing car to produce the very shortest quarter miles time, to brag about it, just before the engine blows up and has to be rebuilt. Many people have simpler needs when it comes to the mods they attach to their airguns. They trust their ears; rather than buying and using expensive calibrated dB meters, in a controlled and approved lab setting, just so they can convince themselves or others that the mod they are using is the best, to the nearest dB. Often in engineering and commerce, the pursuit of perfection is the enemy of good. Settling for good enough or better than expected is not a mortal sin. Despite falling short of the very best possible with a given set of parts. All of whom have been remade to perfection.
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This is an excellent, thought provoking line:
“often in engineering and commerce, the pursuit of perfection is the enemy of good.”
Thinking out loud on this…
If a manufacturer controls the whole “ecosystem” - for example Taipan providing moderators as part of their overall airgun design - then they can pursue/optimize closer to “perfection” tolerances.
If a manufacturer can expect the use of 3rd party add-ons to its product, both the manufacturer of the rifle and the manufacturer of the add-on should consider expected tolerances as part of their designs…
… or so you would hope, lol.
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Cost VS benefit remains a strong driving force; even if the same company makes all components in a given system. At least a single supplier can't blame the makers of other parts.
The end user should concern themselves with the performance of the system, not prescribe how that is to be achieved. If a moderator is quiet enough, light enough and small/short enough, and durable enough at an acceptable price, without grouping degradation or clipping, then the goal seems to be met.
The end user should concern themselves with the performance of the system, not prescribe how that is to be achieved. If a moderator is quiet enough, light enough and small/short enough, and durable enough at an acceptable price, without grouping degradation or clipping, then the goal seems to be met.
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You explained that well. I am fairly new to air rifles but have read up on barrel harmonics, "whip", to use or not to use barrel bands etc and thought maybe I was experiencing something like you described. Especially with the 600mm barrel. I believe in the end my rifle did not care for those particular slugs.
You explained that well. I am fairly new to air rifles but have read up on barrel harmonics, "whip", to use or not to use barrel bands etc and thought maybe I was experiencing something like you described. Especially with the 600mm barrel. I believe in the end my rifle did not care for those particular slugs.
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Blueduck,
Barrel whip is a good way of thinking about it. Barrel bands should shorten the section of barrel that is free to whip; effectively stiffening the barrel near the muzzle. That said, the rest of the design matters, so some barrels can shoot better with bands added, while others may not.
One reason why a barrel band may not help is if it attached to the air tube, and the tube becomes longer at higher fill pressure and shorter at lower pressure. That can cause the barrel to be bent up or down, depending on the air tube pressure, sweeping the point of impact over some vertical distance, even if any given 5 shot group seems tight.
Rather than declare, "there be dragons" with barrel bands, or with free floating barrels. Try a given configuration and see. There may be more variables than the ones we care to consider. Some of them come along for the ride, but can have a larger effect than we imagine, because they are incidental, rather than deliberate variables.
It may be that your airgun needs two barrel bands near each other, to isolate the muzzle end from the section halfway to the breech.
As a for an instance of system dynamics doing strange things, consider using a bipod on a rifle, and which way the legs are "loaded" during aiming. If you push the rifle forwards so that the legs are leaning forwards at the top, then as the rifle fires the rifles is kicked up by the legs, depending on how much it moves back under recoil. If the legs lean backwards at the top, even under forward loading, then the legs cannot kick the rifle up when it recoils. Even when the rifle is kicked up, the groups may shift up, or down, depending on the barrel harmonics induced, and if the barrel whips up or down at the muzzle.
Having barrel whip excited by a bipod that kicks up is undesirable, because variability in the user's hold in preventing rearward travel would tend to open groups. Better to set up systems so they are less sensitive to variability in the user's coupling to the rifle. Not much good to shoot a PCP, if it ends up as hold sensitive as a springer....
Barrel whip is a good way of thinking about it. Barrel bands should shorten the section of barrel that is free to whip; effectively stiffening the barrel near the muzzle. That said, the rest of the design matters, so some barrels can shoot better with bands added, while others may not.
One reason why a barrel band may not help is if it attached to the air tube, and the tube becomes longer at higher fill pressure and shorter at lower pressure. That can cause the barrel to be bent up or down, depending on the air tube pressure, sweeping the point of impact over some vertical distance, even if any given 5 shot group seems tight.
Rather than declare, "there be dragons" with barrel bands, or with free floating barrels. Try a given configuration and see. There may be more variables than the ones we care to consider. Some of them come along for the ride, but can have a larger effect than we imagine, because they are incidental, rather than deliberate variables.
It may be that your airgun needs two barrel bands near each other, to isolate the muzzle end from the section halfway to the breech.
As a for an instance of system dynamics doing strange things, consider using a bipod on a rifle, and which way the legs are "loaded" during aiming. If you push the rifle forwards so that the legs are leaning forwards at the top, then as the rifle fires the rifles is kicked up by the legs, depending on how much it moves back under recoil. If the legs lean backwards at the top, even under forward loading, then the legs cannot kick the rifle up when it recoils. Even when the rifle is kicked up, the groups may shift up, or down, depending on the barrel harmonics induced, and if the barrel whips up or down at the muzzle.
Having barrel whip excited by a bipod that kicks up is undesirable, because variability in the user's hold in preventing rearward travel would tend to open groups. Better to set up systems so they are less sensitive to variability in the user's coupling to the rifle. Not much good to shoot a PCP, if it ends up as hold sensitive as a springer....
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