K-21 Tech Ramble: Hop-Ups and the Magnus Effect

Working On a Mk43 Hop-Up

Introduction

I’ll be bold and say that in my two years in teching airsoft guns, I have found that the most important gun’s internal system is not the gear train or the air compression system, or the electrical assembly but the hop-up. The term “hop-up” refers to the system attached to the inner barrel that provides BB’s flight. This flight is traditionally amplified by a rubber or silicone bump or patch that is designed to make contact with the BB in order to make it spin counterclockwise. In layman’s terms, this counterclockwise motion is known as backspin. The hop-up’s result is most tangible when you watch your BB’s either soar and float in the air a great distance or when you watch your BB’s go limp fish and poop out of your barrel. In other words, the hop-up is the most important factor when it comes to increasing range and accuracy The hop-up is one of the most assessable systems in your gun (mostly – dependent on the system you are running) and is often one of the first places someone begins teching. Mastering how to manipulate and modify your hop-up is one of the key steps to becoming a solid tech. I mean you could master shimming to the point that your gearbox is virtually silent but that’s absolutely pointless if your BB’s are dropping 100 feet from you with five foot groupings.

Prowin Hop-Up System

Magnus Effect and How a Hop-Up Works

The key to understanding the hop-up is to understand the underlying theory behind how the hop-up works and how it provides your BB flight so let’s just jump right into it. When your BB is projected from your barrel, it instantly meets resistance in the form of air. The air’s effect on a spinning projectile is known as the Magnus Effect (or also known as the Magnus Force). This Magnus Effect is the fundamental physics theory behind projecting airsoft BB’s. To save you, the reader, from a lot of unnecessary reading and headaches, I am going to sum this up to a few key ideas:

• If the object is spinning clockwise (top spin), the air’s force is pushing the BB downwards causing the BB to drop quickly and dramatically.
•  If the object is spinning counterclockwise (back spin), the air’s force is pushing the BB upwards causing the BB to arc and rise before dropping
• In airsoft, the Magnus Effect can be amplified or deteriorated by how the contact point makes contact with the BB, how long the contact is for, and how much positive pressure the contact point has.

Remember that when we refer to the Magnus Effect, it only refers to the hop-up and the hop-up alone since the hop-up actually provides Magnus Force for the BB. The barrel is not truly part of the Magnus Effect and therefore the effects of barrel length and inner diameter isn’t part of this discussion.

Classic JG Guide to Adjust Hop-Up

When a magazine is loaded into a gun’s magwell, the BB’s are forced into a tube known as a feeding port. From the feeding port, BB’s are single stacked and pushed into the hop-up chamber, one at a time, by an air nozzle. This air nozzle pushes the BB past the lips of a bucking – a rubber or silicone (or any other soft material) cylinder that is designed to provide backspin for a BB as well as provide air compression to ensure that the air flow is single directional. After passing the lips of the bucking, the BB will pass another portion of the bucking known as the bucking’s bump. This bump is a lump of material that is designed to make contact with the BB to force backspin in order to take advantage of the Magnus Force. This bucking bump is assisted by the hop-up arm (or lever) which is normally a polymer arm that can be adjusted to the user’s preference. At the end of the arm is an object known as a nub. The nub is any material that puts positive pressure on the hop-up bucking. By adjusting the arm, you can determine how much positive pressure you want on your bucking.

How to Take Advantage of the Magnus Effect

So the question comes down to “how do we take full advantage of the Magnus Effect”. To take advantage of the Magnus Effect, we need to fulfil the following criteria:

• Type of contact on the contact point
• Quality of contact on the contact point
•  Length of contact on the contact point
• Quality of positive pressure on the contact point

Now, airsoft gun manufacturers will not go out of their way to produce a good that isn’t cost effective. In fact, it is cost effective for them to only take advantage of incremental innovations such as the V-Hop or the H-Hop purely so they can lower marketing costs (beyond the financial – searching, and resource). As a result, most hop-up innovations can be sourced from the community. There are a lot of DIY projects that is focused on taking advantage of the Magnus Effect. Below are some of the most popular and famous types of modification, both DIY and mass produced. Note that this list is not all inclusive and that this is my opinion of the most popular and famous hop-up modifications.

• U-Hop

• The U-Hop is the most fundamental and basic hop-up design on the market. It is literally a bump of material on the hop-up bucking. The positive pressure on the hop-up is normally provided by a cylinder shaped rubber nub. This design is fundamentally good but lacking modern innovation. All airsoft companies produce these in varying degrees of quality.
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  Standard bucking and nub configuration

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•   V-Hop/Nubs

• The V-Hop looks like a U-Hop with a split down the middle of the bump. The focus of the V-Hop is to center the BB to maximize stabilization and eliminate variability in the BB’s flight. This elimination in variability helps amplify the Magnus Effect.  
  
  

  

  Classic V-Hop

  
  

  

  
  

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•  H-Hop

• The H-Hop focuses on the nub rather than the bucking. The nub looks something like an hour glass. The idea of the H-Hop is similar to the V-Hop. It is designed to center the BB to maximize stabilization and eliminate variability in the BB’s flight. This elimination in variability helps amplify the Magnus Effect. However, the H-Hop is designed to curve around the BB rather than having two rigid contact points which gives it more contact surface.
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The weaknesses of these two methods are the contact period with the BB. The amount of time the BB actually spends in contact with the hop-up is extremely minimal. This results in a shift from circular groupings to oval shaped groupings. The multiple contact point’s idea causes more centered backspin, but a less consistent amount of backspin leading to more vertical groupings.

Flat Hopping a Bucking

• Flat Hop

• The flat hop focuses on increasing the length of contact. By elongating contact, the BB’s flight is amplified since the elongated contact adds faster backspin. This results in long range and the Magnus Effect being amplified. This modification can be done by flipping your current bucking inside out and removing the bump. After this, you need to install a rectangular nub. This will even the amount of positive pressure throughout the entire contact space. In fact, whenever you elongate contact, you must use a flat hop nub or something of the sort. As of recent, there are mass production attempts at the flat hop with decent success. The Maple Leaf bucking is one that comes to mind but further detail will be saved for a future review down the road.

Prometheus Purple DIY Flat Hopped Bucking (Work in Progress)

Maple Leaf's Decent "Proprietary" Design

• G-Hop

• The G-Hop is essentially gluing pieces of bucking together in order to make a longer contact patch. This is one of the first uses of “patches” that went into the barrel windows. The patch would be made of different buckings. I won’t go into this too much since I only attempted this about three times and I found that this type of hop-up was prone to install inconsistencies and reliant on each piece staying glued. 
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Finished G-Hop

• J-Hop

• The J-Hop is actually one of my favorites. The J-Hop traditionally uses materials such as silicone filament in order to fill the barrel window. The goal of the J-Hop is to create a customized mold to perfectly install a contact patch. This patch theoretically will make the BB more accurate since it's shaped exactly to the barrel. The only issue with this is that it is time consuming and the traditional materials are not very durable.
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J-Hop Work in Progress

• R-Hop

• The R-Hop is the most popular and famous among the highest of teching sub-communities. After experimenting with the G-Hop, Hunterseeker5 created a patch made out of certain materials that elongate contact as well as provide concave contact for the BB. The exact material is unknown (but close estimates have been found) and the R-Hop has spawned its own theory known as the “wobble hypothesis” to explain its success. It's important to note that the wobble hypothesis borrows heavily from the Magnus Effect. 
  The R-Hop is a durable way to separate the air seal component of the hop-up bucking from the contact component of the hop-up bucking while still drastically increasing range and accuracy. To sum up why HS5 believes the R-Hop is so successful, “when fired the R-hop's extended contact and concavity prevent the round from shifting side to side or up and down.” This shifting that HS5 is referring to is from the variability in each BB. Each BB is not made equally (as in each BB has a sizing and weight variance) which has led to a fundamental issue with range and accuracy. HS5 believes that he has minimized BB “wobble” with the R-hop’s design.
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R-Hop Work in Progress

Now, realize that I went over a ton of information so don’t feel bad if this is blowing your mind. It is a lot of information to soak in at once. However, realize that your understanding of the Magnus Effect will effectively make you a better theoretical tech and it will allow you to more appropriately tech on your airsoft guns better.