Hop units and Hop Rubbers

The hop is everything to airsoft, snipers twice as much. For those new to it, the hop bucking or rubber is a rubber or silicone mound in a window on the inside top of your barrel, that the bb brushes past to generate backspin. Without backspin, the bb wouldn’t travel very far at all. But, it does more than just that. It holds the bb in place prior to the shot, gives a good airseal, and controls not only the range but also the consistency and grouping of the shots. I’ve seen it described as the “brains” of the gun, and the importance of a good hop setup cannot be understated. So, how do you get it right?

Well, firstly lets understand what hop is and what it does, and how it’s applied;

Don’t drink and set hop up

Fairly simple. The hop arm is adjustable from the outside of the rifle (usually) so the player can turn hop on or off. It will have a mechanism that pushes the arm down onto a nub, that in turn presses down onto the contact patch which fits over a square window in the top of the barrel. When the bb brushes past, it grips the bb and forces it to start spinning so that it fights the urge to drop out of the sky for longer. All in all, it should be a very simple operation, but there are a lot of small variables that need eliminated, because a tenth of a mm off at the gun end can mean a few metres off at the target end. Understanding what can go wrong and how to fix it makes the difference between a good rifle, and a bad one.

A lot of people will begin by buying a whole new upgraded hop unit, but the more important piece here is the hop arm, although some are integrated now into the unit itself but can still suffer the same problems. The hop arm needs to stay central as it pushes down on the nub, and unfortunately most stock hop arms are either plastic (will flex) or just don’t quite fit the allocated gap in the hop unit properly, so when firing can jump left or right. The effect of this is that you don’t put 100% backspin on, it’s kind of 80% with 20% side spin, which causes that most common of bolt action issues – the left or right curve. Much the same as when you swerve a ball in pool/billiards/snooker, the effect of the spin is increased as the ball/bb starts to slow down and lose power (at the end of the shot). So you often see the bb travelling straight towards the target, before suddenly just veering off to one side. There are a few causes for this, but sorting the hop arm out is a great place to start.

Because your stock gun is made as cheaply as possible, as a package, things will need replacing. Generally speaking, the hop unit itself isn’t responsible for a lot, it’s the arm that is important. A cheap but very effective upgrade is an improved hop arm. These are usually CNC machined steel, so will not flex under pressure, and are made slightly wider to fill the gap in the hop unit much better and eliminate left and right movement. Here’s a common example, the Panthera hop arm from Stalker for the VSR;

It’s a much cheaper option than a full new hop unit and puts solid, consistent pressure on the nub. The next upgrade you may want to consider is a TDC (top down centre) modification. On most rifles, this will replace any wheels, sliders or screws that are used to tighten the hop arm down onto the nub, with a screw type adjuster (on homemade TDC’s, is actually just a screw) on the outside of the barrel directly above the contact patch, so that the pressure is then applied directly downwards, right in the middle, which will improve accuracy and consistency of the applied pressure. I use the absolutely excellent Gunsmithy TDC;

One thing to note with TDC’s, of which there are a few on the market now, is that some are only 3D printed plastic, and some adjust in “clicks” or stages, and that can mean that you miss your sweet spot because it’s inbetween two different clicks. The better ones are the ones without clicks, to allow infinite adjustment.

If you’re shopping for hop buckings, one of the first things you’ll see is the hardness, expressed in degrees (no, it’s nothing to do with angles). Usually 50, 60, 70, 80 degrees, the higher the number, the harder the bucking material and therefore the more durable. The lower the number, the less durable, but the grippier the material, and it’ll add a lot more spin to the hop.

That’s so you’ll remember it. So what if it wears out faster and you need to replace it perhaps every year? Much better to have had improved performance during that time.

Good airseal is important for consistency. Even if your shots are slightly off, at least they’re hitting the same spot so you can adjust. The other thing to look at is the contact patch (go back to the second diagram at the top). Basically, this is the bit that contacts the BB, and the longer it is, the more spin it will put on. Some buckings will have tapered patches to “guide” the BB and keep it stabilised in the centre of the barrel, which is a good thing. Already in the few weeks I’ve been compiling this upgrading section, there have been two new buckings released and so I’m not going to rattle off a list of what’s hot and what’s not because it’ll be out of date quickly. What I will say is that Maple Leaf and Modify are the market leaders and you’ll rarely go wrong with either. Checking in facebook groups for bucking conversations is usually the best way to keep up, and do consider the right nub for the bucking too – they come in different shapes to help “mould” the contact patch correctly; for example if it is a concave contact patch, you want a nub that will push down and maintain that shape.

Always use a hard nub. Softer nubs (rubber/silicone) will deform under the pressure of the shot. One of the best mods in the earlier days was to cut a section of the inner plastic tube of a biro pen, and use that as a nub, as it was a hard, straight piece of plastic that didn’t deform.

Get the hop set up correctly, and you’ve got a good rifle. Get it wrong, and you’ll hit nothing. Thankfully, it’s cheap to swap bits out.

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