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.
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.
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.
