The bucking is a piece of rubber found inside the hopup chamber of an airsoft gun. Airsoft guns equipped with a hopup can achieve much further range than an airsoft gun that does not have a hopup. This is because of the backspin that the bucking/hopup chamber puts on the BB as it is fired and exits the barrel. Airsoft guns fire a round projectile through a smooth bore barrel, which is significantly limited in range without hopup. That backspin that hopup produces counteracts the forces of gravity with something called the Magnus effect, which in turn increases the range of the BB.
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Being that the bucking is made of rubber, this part can wear out, dry up, or tear over time. This part is considered a part you should replace every once in a while for an airsoft gun that is meant to be used and enjoyed quite a bit. Bucking maintenance should be done with 100% pure silicone oil. This keeps the rubber conditioned so it does not harden over time or dry out as fast. Any time that happens, you're almost guaranteed that the bucking will tear, whether it be on its own or if you need to do something about it.
A bad bucking can be signaled by many things since this is a vital part of the gun. The bucking holds the BB in place before firing. The bucking provides a backspin for the hopup effect. The bucking seals against the nozzle from the gearbox, which directs air from the piston/cylinder to the BB. If you experience feeding issues, the BB rolling out, or a loss or fluctuation in FPS, these can all be traced to the bucking if everything else is mechanically sound.
Looks like I need a new bucking! This one is over two years old, but you could/should change it every time you have your hopup apart to be safe. I would like to change it from once a year to once a season if I use this gun frequently enough.
Sometimes, you could encounter a brand new gun with a problematic bucking, and that could be enough to cause issues. This is not common, but you might see it on extremely cheap guns, which coat the internal parts excessively with grease and use very thin rubber buckings.
How do you look for a good bucking? If you are looking to replace your bucking, first, be sure the bucking you are looking at is compatible. A good bucking will be soft to the touch. Thicker ones could seal better and last longer; however, you might have trouble installing them in a tight hopup chamber. Bucking manufacturers sometimes mention a rating that tells you how hard the rubber is. On guns that shoot harder, such as DMR-type guns, you would want a slightly harder bucking so that it will last longer. Softer buckings would get eaten up by a hard shooting gun. However, soft buckings are ideal for lower-powered/CQB-type guns. Our favorite and most recommended bucking compatible with most AEGs is the Madbull Blue Bucking. We offer them as part of our accuracy packages that we install in people's guns. If the hopup chamber for a gun is too tight to fit a Madbull Blue bucking, we default to other aftermarket brands such as ICS and some others. If you are removing your bucking, typically, you should replace it with a new one anyway. The old buckings tend to get torn in this process if they are very dry or at the end of their life cycle. New ones are not so much; however, I have seen that on Ares buckings, they could easily rip if you aren't extra careful. I would take the opportunity to upgrade anyway.
The bucking and barrel for an M4-style AEG is one of the easiest tech upgrades you can attempt to do yourself. You do not have to open your gearbox, and you can enjoy some noticeable effects with a new bucking, such as increased accuracy and better air seal, which could mean more FPS and more consistent performance. If you are looking to learn how to teach your own guns, this is the place I would start because you won't cause any damage to your gun, unlike taking apart a gearbox and putting it together wrong. The worst thing you can do is damage a bucking or install a barrel improperly, but even then, those are easily corrected. Do this on a gun that is not under warranty and with the supervision of somebody qualified, or be sure you have a backup plan in case you do something wrong.
An M4 hopup chamber from a Lancer Tactical M4. This is what is known as a rotary-style hopup unit due to the big adjustment wheel.
This is another rotary hopup unit found in an Elite Force competition series M4 rifle.
This is an AK hopup unit that uses a sliding lever. It is very simple, but AK hopup units provide some of the most dependable and consistent performance.
A quick word on accuracy: a good bucking/hopup unit should be reasonably consistent in accuracy, not counting crosswinds. If you run a heavier-weight BB, you should be able to notice it right away. A better bucking should only serve to tighten your groups a tiny bit and keep the patch of your BBs pretty consistent. If you are noticing shots consistently curving to a side, you might have a situation where your bucking and nub are not centered, causing the hopup to bias in one direction. You can inspect this by taking the barrel/hopup chamber out, turning on the hopup a little bit, staring down the barrel, and then making sure it is centered. The effects of it not being centered are going to be magnified greatly as the shot exits the barrel.
Barrels and Buckings
Aftermarket barrels such as this trusty Madbull Black Python serve to improve range and accuracy by giving your BB a tighter constriction to travel to. Stock inner barrel diameters range from 6.06mm and greater. Tight bore barrels usually come in at 6.03mm, 6.01, or even 6.00 in some extreme cases.
That's all I have for you on buckings today. I hope some of this information is applicable to you and that you can move on to improving the accuracy of your own AEGs.
The terms ‘HOP-up’ or ‘HOP-up bucking’ are mentioned regularly in airsoft and as a player, it’s important to know what one is and how it functions. We’ve put together this handy hop-up bucking guide so you can find out everything you need to know. You’ll learn how to choose the best HOP-up unit, so you can tune your AEG perfectly and get the best bang for your buck.
The HOP-up, or ‘HOP’, inside your AEG, Sniper rifle or GBB provides backspin to the BB as it enters the inner barrel, allowing the BB to travel further and with greater consistency. There are two main types of hop-ups available, either AEG type or GBB/VSR type.
When a BB is loaded, it comes in contact with the HOP-up bucking which causes friction on one side of the BB. This provides backspin to the BB, allowing it to travel beyond the point that a gun without a HOP would reach. As a result, the gun achieves a greater range, while still maintaining non-lethal power levels.
Put simply, the Magnus Effect is the observable behaviour of a spinning object as it travels through Air, which cannot be observed when the same object is not spinning. This relates to differentials in Air pressure caused by the spin, similar in principle to the Aerofoil effect observed in the wings and control surfaces of an Aircraft. But enough with the Physics lesson, as it relates to Airsoft the Magnus effect can be observed in BBs provided with backspin through contact with a surface which causes friction on one side of the BB (the HOP bucking), extending the range and providing an upwards force allowing the BB to travel beyond the point that gravity alone would have it fall.
In principle, all adjustable AEG HOP units work in a very similar manner and many share common buckings and nubs. Obviously, if you are fresh to the sport of Airsoft, this doesn't make anything less complicated, so here in this blog we will outline the components of a HOP unit, get you up to date on terminology, and the pros and cons of using particular HOP-units over others. Compatibility-wise, there are two main types of hop rubber/bucking available, either AEG type or GBB/VSR type, and whilst they differ in appearance they provide the same function for each platform. Having such a wide range to choose from may sound daunting if you’re new to Airsoft, so we’ve included all the terminology you’ll need to know in this hop-up guide.
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The bucking is the rubber piece that makes direct contact with the BB during firing, providing backspin and extending the range of your shot. These are usually in the form of a small rubber tube of varying hardness that goes over the chamber end of your inner barrel, interfacing with grooves cut in the chamber end of the outer surface of the barrel. The hop bucking you choose will largely depend on what FPS your replica shoots, or your target FPS for your build. The harder the bucking, the more effectively it will apply hop to higher FPS replicas. The reverse of this is also true, as a harder material will decrease the effect of the HOP-up on lower FPS builds.
The nub is the component that pushes on the Bucking when it itself has pressure applied to it by the arm and adjuster. This is usually in the form of a tiny plastic or rubber cylinder but can is also offered with a flat surface on one side, or with a groove down the center in more specialized nubs. This part allows the amount of contact the bucking has with the BB to be varied as the nub pushes through the "HOP window", a usually square hole machined into the chamber end of the inner barrel. Variations of HOP nub and their uses can be found below:
The H-Nub is one of the more common HOP enhancements available. This type of nub is cylindrical but with an hour-glass shape or "H" profile, and aims to provide more stable HOP application by applying pressure evenly to both sides of the BB. These are suitable for any AEG and can be easily installed, with effective results.
The Flat Hop Nub is a nub with a rounded side, to interface with the adjuster, and a flat side to put pressure on the BB. The theory behind the flat nub is that its larger contact surface will provide greater pressure and allow a greater level of hop to be applied. Flat hop nubs are designed for high FPS builds and DMRs which use heavier BBs by default, but can require a lot of fine-tuning to set up well.
R Hop refers to a small patch of rubber that can be installed over the inner barrel window before the bucking is installed and effectively increases the HOP effect by adding further pressure to the BB. These patches usually need attachment with glue and are prone to failure, but provide a significant increase in range and accuracy when done right.
The Adjuster is the part you will physically turn or move, to increase or reduce the amount of HOP up force applied to your BB. This can be found in several forms. The more common types found on AEGs are the Gear, Rotary, and Slider. These are generally found either in or near to the chamber area of your Airsoft AEG and are sometimes concealed behind a small door or the mock bolt carrier should your AEG have one. The most common types of adjusters are listed below:
Gear Adjuster - The most common type of adjuster for M4/AR15 platform AEGs. Gear adjusters are easy to adjust quickly but are not as easy to adjust in fine increments. The gear adjuster is one of Tokyo Marui's earliest designs, and as such it has a plethora of replacement enhanced units available and has proven itself reliable over its nearly 3 decades of use. Gear adjusters can also be found in some HK33 and SMG5 replicas. Gear adjusters are also prevalent in GBB pistol replicas, primarily due to the space confines within the internals of a pistol.
Slider Adjuster - The most common type of adjuster found on AK47/74 replicas. Slider adjusters are not as quick to adjust from zero to full HOP as the gear but provide a greater ability to adjust the unit in small increments. These have been on the market since Tokyo Marui released its AK47, AK47 Beta Spetsnaz, and AK47S in the late s. Slider adjusters are also used on older designs of SMG5 replicas.
Rotary Adjuster - The rotary HOP unit was first used on the Tokyo Marui AUG AEG and has since found its way into the majority of AR36, P90, AUG, and G3 AEGs. The Rotary HOP adjuster allows a great middle-ground between quick adjustment and accurate fine adjustment and applies pressure on the nub directly from above. This minimizes the possibility of applying uneven pressure to the nub which is a common cause of inaccuracy at long range. The Rotary unit is widely regarded as the best design for these reasons, and more recently designed M4/AR15 AEGs now features a Rotary type adjuster.
TDC Adjuster - TDC stands for top dead center, meaning the adjuster is positioned directly above the point of contact where the nub meets the rubber. This is most commonly found on sniper rifles and can be added as an aftermarket option to those which don't include a TDC out of the box. TDC adjusters began their life as a homebrew option for accurizing sniper rifles and NBB pistols, and provide the absolute most precise adjustment for your HOP. This comes at a price, however, as TDCs adjust via a grub screw and as such they will need a very small Allen key to adjust, reducing their ability to adjust during an engagement in the field.
The HOP up Arm is the piece that transfers the pressure from the adjuster to the nub. These are available as reinforced parts, and whilst there is no harm in upgrading this piece as a preventative measure, reinforced HOP Arms would generally be more useful in high-FPS builds which will cause more wear and tear on the Arm by their nature, especially when used with a considerable amount of HOP applied.
The HOP chamber/unit refers to the piece which receives the BB when the magazine is inserted and houses the HOP parts which apply the backspin to your BB. When shopping, this term is often used to refer to a complete unit and also a bare-bones unit for which you will have to use the small parts from the unit you are replacing. These are available in polymer, Alloy and CNC machined aluminium for various AEG and Sniper rifle platforms. The material you choose doesn't really matter, as the most important thing a hop unit can provide is a tight fit and good air seal. There are advantages to using a metal hop unit, for example, they are less prone to breaking, especially if you use a metal nozzle or a high rate of fire setup, and CNC units provide an immaculate fit which can only really be achieved with precision-engineered parts. For the most part, polymer units function perfectly fine and are often the only part of the HOP set up which I personally don't recommend changing, other than in the case of high rate of fire builds.
The hardness of a HOP rubber is a metric for how much backspin the HOP unit will apply to BBs traveling at a certain velocity. Most out-of-the-box AEGs of UK power levels should be using a rubber of hardness between 50 and 60 degrees. Generally, the softer the rubber the more HOP is applied, though this comes at the cost of the softer rubbers wearing out more quickly and often providing too much backspin when used at higher velocity levels. Higher velocity setups may require harder HOP rubbers, as the impact of the BB hitting the hop rubber will be much heavier and may cause tears in softer rubbers. As the Magnus effect depends largely on the velocity of the spinning object, you may find that when upgrading to a DMR level of FPS you will have too much HOP effect, even when using heavy BBs. If this is the case you will need a harder rubber. For standard AEGs firing at around 350 FPS or under, a 50 or 60 degree HOP is what you will need, as any higher may see your HOP effect reduce. If you are upgrading your AEGs hop, the hardness of HOP rubber you will need depends entirely on what you aim to achieve with your setup. The following list outlines the requirements for approximate rubber hardness to match setups firing at a range of FPS.
Recommended HOP rubber hardness / Velocity combinations (0.2g BBs)
To get the most out of your Airsoft rifle you will have to set the HOP unit for the BB weight you are using, ensuring a flat trajectory and thus maximum effective range. In order to adjust your HOP unit, you will need a minimum of 30 meters safe range to shoot, either on your own property or with the property owner's permission, out of public view. Preferably this should be carried out when there is little to no wind, to make the job easier. Of course, you will need the obvious, BBs and eye protection.
The first step will be to load your Airsoft gun with the BB weight you intend to use for Skirmishing, point it downrange, and shoot, paying attention to the trajectory of the BB. If the BB suddenly arcs downwards during its flight you have been a victim of gravity, and you need to increase the HOP effect by dialling your HOP unit upwards (some units are marked with +/-, others it will be trial and error). Once this has been done, fire again and observe the trajectory. If the BB now flies upwards, you are now shooting a mortar and you will need to back down on the adjustment. If the BB flies straight and flat, you have achieved a flat trajectory and thus, a perfectly set HOP up. Repeat this process until you have a nice, flat trajectory, and your Airsoft gun is ready for combat.
So perhaps you are wondering what we prefer to use in our own Airsoft guns? Sticking to a standard AEG sub-350 FPS setup, my personal preference in bucking/rubber is Guarder Clear 50 degree HOP buckings. These buckings are my preferred choice simply because they have been around forever and have always served me well. Being made from softer rubber, these can handle cold weather without losing too much performance, are decently robust and last for a good length of time, and are fully compatible with the vast majority of nubs available, though Guarder does include a basic soft nub with the bucking itself which works perfectly.
With a Guarder bucking installed I have always been pleased with my AEGs range and consistency, and have found they perform much better than stock HOP rubbers on more affordable replicas and are about the cheapest effective upgrade for AEGs available. As far as nubs are concerned, I prefer to use H style nubs, as I have found they offer a good balance between consistency and reliability. Whilst they may not provide the performance a Flat HOP or R-HOP are reported to have, I have had no issues with jams or compatibility. Since the design is well within the parameters of the original AEG nub design you can drop an H nub into your HOP unit without any risk of having the window in your barrel be too small, or your rubber being too inflexible. That and they require far less care and maintenance than Flat and R-HOP nubs, meaning more time shooting less time messing.
As far as replacement HOP chambers/units are concerned, I am currently using a ProWin AR36 CNC Hop unit in one of my many G36s, and it is performing nicely, providing a slight FPS increase due to the improved air seal from this precisely machined unit. I bought this to replace a unit I accidentally broke during disassembly, and though I generally don't upgrade the unit itself in my guns, I found that the ProWin CNC Hop unit provides enough improved performance and consistency to justify installing in a replica you want to get the absolute best from, particularly if you are building a DMR or other accurized setup.
There you have it! Our guide to HOP-up, what you need to know and how to get the most from the HOP inside your gun. This applies primarily to AEGs, though the principle is the same across all Airsoft Gun types. A more detailed guide to HOP disassembly and installation of rubbers and nubs is yet to come, so until then, good hunting!
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When using a laser alignment system to check a machine or sub-assembly for straightness, flatness, bore alignment and many other geometric parameters, we often need to normalize the laser reference beam to some designated locations on the surface being measured. The laser reference beam is very straight and true but may not be aligned to the surface or mechanical features that you are measuring or checking. For example, imagine a guide rail that you want to check for flatness and at one end of the rail the laser is 2 inches above the rail surface and at the far end of the rail this distance is 2.5 inches. Intuitively, we would like to adjust the laser reference beam until it is a common height above the rail and then make our measurements.
However, the rail surface is not necessarily straight so we need to designate two locations on the rail, called datums, that we can use to establish a straight reference line. We were all taught that “two points in space define a line”. It is at these two designated points, or datums, on the rail that we use to “connect” the straightness of the laser reference beam to the surface that we are trying to measure. This step is frequently referred to as “normalizing” and is in many ways similar to calibrating or connecting the measuring system to the surface to be measured.
We can start by measuring the position or height of the straight laser reference beam relative to the rail surface at two designated locations. At these two locations we have a precise Laser Microgage reading of height and we also know the distance from the laser transmitter to the designated location. Now, we have two options to normalize the position of the laser reference beam to the surface we want to check; bucking in the laser or leaving the laser beam where it is and using math to normalize the readings. Both methods have their advantages and disadvantages.
First, we will consider “bucking in” which is the process of steering the laser so that the laser and the surface are physically parallel to each other at the two designated datum locations. The “bucking in” approach is iterative and involves moving the laser transmitter and/or the surface being measured and re-measuring the values at the two designated locations. This process continues until the readings at the two locations are the same indicating that the laser reference beam and the surface datums are now parallel. The measurement values may not be zero and this is easily achieved with a zero function on Pinpoint’s Laser Microgage display units. The advantage of bucking in the laser and the measured surface is that the receiver can now be moved anywhere and readings that deviate from your zero value indicate high or low regions on the surface being measured. The disadvantage of the bucking in process is that it takes time and sometimes requires finesse to position the laser beam in exactly the correct position and repeat the measuring process. Over the years we have found that many Pinpoint customers have used this process with traditional instruments and prefer to continue with this method.
An alternative to the “bucking in” process is to bring the laser beam generally close to parallel with your two designated datum locations and then use math to calculate the position of the laser beam above the surface that is being measured. Based upon the two selected datum locations on your measured surface, the math involves calculating a rise over run value, commonly referred to as slope, which can then be applied to all the other measurements taken. Based on this information you can now calculate exactly what Microgage reading you should be seeing for each given location on the surface if the surface were exactly straight. The difference between this calculated value and the measured value that you obtain from the Laser Microgage tells you the surface error and which direction (up or down) this error is occurring.
For example, consider a laser reference beam that is not exactly parallel with a machine surface but with your Laser Microgage Receiver, you record a height value of 0.005 inch and 0.010 inch at locations that are 20 inches and 40 inches from the end of the surface, respectively. A simple calculation tells you that halfway between 20 and 40 inches the reading should be 0. inch. If your Microgage measurement does not produce this value then the difference tells you the error in the straightness of the surface and also the direction of this error. Measurements can be made in many places along the measured surface and compared with the calculated values to find the difference in the values or delta values for the surface being measured.
The advantages of this mathematical approach is that it reduces the time needed to “buck in” the laser and is very accurate for measuring. The disadvantage is that for each measurement made you also need to record the position or distance of the laser from the receiver for the calculation at that location. At Pinpoint, we have spreadsheet applications and other tools that make this process quick and easy.
Using a computer or laptop and Pinpoint’s interface option and Capture software you can record many readings and run the calculations quickly and accurately. The Microgage can be set to record readings at a set interval and export these readings into a spreadsheet application. If the Microgage receiver is moved at a fixed rate, and the readings are recorded at a set time interval, one can gather hundreds or thousands of readings along a moving slide or surface and see with great detail how straight the travel or surface really is.
We have talked about the Bucking In process and normalizing measurement readings by measuring distance and using mathematical techniques for each reading. Both methods have their advantages and disadvantages and we have worked for years with customers that are comfortable with one method or the other and with great success. We encourage questions and comments on these methods and have full write-ups and spreadsheet applications to help with each.