Author Topic: Tech Ref 01: Hop up position & bb impact points, The bb flight path  (Read 1164 times)

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Offline moky

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Hop up components -- namely the hop up bucking, the nub, the adjustment lever, and the hop up chamber itself -- are at the heart of your AK's accuracy. Not all hop up mechanisms are exactly similar but the named components are essentially the same for all existing varieties and these will be sufficient for the our discussion.

Let us start by looking at the bb's flight path. Many of us imagine the bb as traveling in a straight path to our point of aim like this:


But if we look at the the bb travel through the air from the side, we will find that, in reality, our aimed bb goes like this:


And this where our hop up, specifically our hop up bucking and nub, becomes very valuable. We can adjust the amount of pressure the bucking exerts on the top of the bb to shape the arc of the bb's flight so that our point of aim and the impact point will coincide, more or less, at a specific distance from the muzzle of our AK.

If, for example, we have zeroed our AK for 15 meters with proper hop up adjustment, we will get these impact points at 5m, 10m, 15m, and 20m.


In this case, the nub of our hopup will be sitting right on top of the crown of the bb:


Now, what happens if, either by mistake or some slipup, the nub center is nudged to the left? We will then get these impact points at 5m, 10m, 15m, and 20m.

Similarly, if the nub center gets nudged to the right, we will get these impact points at 5m, 10m, 15m, and 20m.


Notice anything peculiar?

You got it! The impact points climb up in the direction of the skew and, after reaching its flight apex, seems to reverse direction relative to the vertical axis as it loses momentum and begins falling down to earth.

If you find it difficult to picture this, draw an arc approximating the flight path of the bb lengthwise along the middle of a piece of bond paper. Set the lower edge of the paper upright on a flat surface. Then tilt the paper about 15-30 degrees right or left. Follow the arc along the tilted paper. Look at how the arc appears to you.

Up in the direction of the tilt up to the apex of the path, right? And then down in the reverse direction, correct?  Always along the plane of the paper.

Perhaps this is one of the reasons your groupings sometimes worry you and makes you look for something troublesome? When after all it is just normal bb behavior?

We have to keep that flight path picture firmly in mind. That will be very useful when we take up BB Flight Behavior Analysis in Tech Ref 02. Here are the skew left and right impact points again. Together, this time, for easy comparison.

Sometimes it is neither the bucking nor the nub that is mispositioned. The hopup chamber might be skewed, either through improper installation or, if you're unlucky, some sloppy QC in the production or assembly process.

When this happens, we get off-center hits and bad groupings. A misaligned chamber can also result in misfeeding, another issue we will take up in a future Tech Ref post.

Courtesy of our fellow airsofters at  ;D
« Last Edit: October 21, 2008, 08:42:02 AM by moky »