Maruzen CA870 Charger NEW HOP Custom and Mechanism Explanation

Last time, in the Maruzen CA870 Charger NEW HOP disassembly (custom order), we completely disassembled it.

This time, we'll make adjustments and customizations based on the areas for improvement we identified last time.

Let's review the areas for improvement, customization methods, and parts procurement.

Improvements, customization methods, and parts to procure.

To recap, let's list the areas for improvement.

To address this, we decided on the following customization method.

The parts we have procured are as follows:

Photo of parts used

We will carefully assemble these parts.The parts I ultimately used will be listed in the recipe at the end.

Let's actually get started. By the way, the assembly method is the reverse of the disassembly method, so if you get stuck during assembly, please refer to the previous article. The link is at the very top of this page.

Since scrolling back every time can be tedious, there's an icon in the bottom right corner of the screen that looks like a circle with a "V" inside; touching that will take you straight back to the top.

If you get stuck on the assembly process halfway through this article, please try using this resource. Alternatively, it might be helpful to have the browser tab open alongside the disassembly section.

Main unit, gearbox adjustment, customization

First, we'll polish the sliding parts of the main body's casing. These are the blue parts in the photo.

Since these are basically cast parts made using molds, the surface is very smooth (surface thickness 12.5-25μ), but we polish them for better operation.

Polishing by hand is a pain, so I'll use a rotary tool to buff it.

Even without a rotary tool, you can do it with sandpaper, though it will be difficult.

After polishing, it will look like this.

Polishing the ammunition supply route is especially easy to forget.

While feeding problems are inherently rare, we take the time to improve them even further.

Dremel High-Speed ​​Rotary 4000
This is my go-to rotary tool that I always use. Having this expands the possibilities of your DIY projects. There are two popular models, the 3000 and the 4000, but I recommend the 4000 because it comes with a set of tools and has more power.

Next, we'll install the non-bound springs 0.9J.

First, let's compare it to the original.

The non-byne spring is shorter and has a narrower spring coil pitch. Furthermore, it's an unequal pitch spring.

This is the base section. It has been thoroughly polished.

As someone with an engine design background, polishing the spring's coiled section is standard practice, so I'm not entirely convinced about the quality of the genuine parts (it doesn't cost that much).

As a side note, I spent quite a while designing engines for race cars. I struggled a lot with springs (valve springs, etc.) when trying to achieve high power output and high RPMs. There was a time when I thought about springs all the time, whether I was awake or asleep. So I'm a bit picky and particular when it comes to springs.

We'll now assemble this into the spring guide.

To prevent spring noise, I'll apply some silicone grease to the springs as a precaution.

AZ Silicone Grease
This is a standard product from AZ. While Tokyo Marui's genuine grease is sufficient, the quantity is small, so AZ is recommended. It's also inexpensive.

We will now assemble this into the main unit.

Next, we'll apply grease to the piston and the inside of the cylinder.

I'll be using the standard GAW G-Grease.

GAW G-GREASE
This is a standard grease. It has a lower viscosity compared to the Bellhammer Gold series, so I use it inside the cylinders of both electric and airsoft guns. It's a bit pricey, but the quantity is large, so in the end, it doesn't feel overpriced.

Apply this to the inside of the cylinder.

Apply it to the packing at the tip of the piston as well.

We'll temporarily assemble this and move it around to let it settle in.

We'll assemble this into the main body while applying a different type of grease.

Apply Bellhammer No. 0 Gold Grease to the sliding parts (No. 0 is often used for metal-plastic parts).

Bellhammer No. 0 Gold Grease
This is a classic, top-quality grease. No. 0 is a low-viscosity grease. I generally use No. 0 for resin-to-resistance and resin-to-metal connections.

After applying the grease, move each part to distribute the grease evenly.

Next, we polish the sliding parts of the trigger-related components.

The process is the same as for the main body: polish it with a rotary tool. This extra step won't affect the trajectory, but it's recommended because it makes the trigger feel smoother.

Assemble this while applying Bellhammer No. 2 Gold Grease (No. 2 is often used for metal-to-metal parts).

Bellhammer No. 2 Gold Grease
This is a classic, top-quality grease. No. 2 has the same ingredients as No. 0 but with a higher viscosity. I primarily use it for metal-to-metal connections.

We will carefully assemble the trigger-related parts.

Since we're on the subject, let me briefly explain the mechanisms of triggers and shears.

This is the uncocked state. Please pay attention to the sear.

When this is cocked, the sear holds the white part (piston) in the retracted position.

When you pull the trigger here, the sear bows forward via the link and releases the piston.

The piston moves forward and the bullet is fired.

From an industrial perspective, it's a simple latching mechanism using links. I think its simplicity contributes to its reliability and smooth operation.

The mechanical parts are now complete.

Hop section modification and customization

Next, we will proceed with the renovation of the hop section.

First, to improve the movement of the hop-up arm, apply Bellhammer No. 0 Gold Grease.

You won't see any major changes, but the arm's movement will improve slightly.

Next, we'll do some minor modifications to the inner barrel.

Let's take a look at the hop-up window section of the barrel.

No matter how excellent the manufacturer, burrs and edges will remain unless a deburring process is included, so we remove them. From a cost perspective, an inner barrel without these burrs would likely cost over 6000 yen.

The method is simple: trace the window with a round diamond file.

Diamond file set
These diamond files offer great value for money. The round files, in particular, are very useful. The 5-piece set is highly recommended.

This is the photo after the removal. You can't really see the difference in the photo, can you? (laughs)

Next, let's take a look at Miyagawa Rubber's Hop Packing Hanamaru Nitrile Rubber, which we plan to change to.

It features a bifurcated protrusion shape, a detail that Mr. Miyagawa insisted on.

Let's compare it to the original.

Mr. Miyagawa's attention to detail in the gaskets resulted in thicker rubber and a firmer feel. It seems like a good product. I forgot to take a picture, but the gasket opening was also thick (compared to the original).

As usual, I'll apply AZ company's silicone grease to the hop-up barrel and assemble it.

Here, we check to make sure the gasket is assembled correctly.

We will now carefully assemble this into the main unit.

The grub screw that pushes in the hop-up arm can be installed after the main body has been assembled.

Apply Bellhammer No. 2 Gold Grease to the rail sliding surface of the foregrip that you cock.

Once this is assembled, the main unit is complete.

Now close the device.

Once you've closed the unit, check that the hop-up arm moves correctly, and you're done.

Now that it's ready to fire, let's check its operation.

Functionality check and correction

Now we'll check the operation and initial velocity.

We'll check the initial velocity with 0.2g BBs.

This is nowhere near our goal, so we will be making improvements.

If I were to guess the causeI simply thought that the spring load was too low (shorter than the original), the hop-up packing was too hard, resulting in excessive hop-up, and the packing was too thick, preventing the nozzle from gripping the packing properly.

As a solution, I decided to revert the hop-up packing back to the original and increase the load by raising the spring height.

I'll put the original hop-up packing back in.

As usual, in addition to AZ silicone grease, I'll also wrap it with the standard KAKUDAI sealing tape to prevent air leaks, since the rubber is on the softer side.

KAKUDAI Seal Tape
This is a standard item for ensuring airtightness in all kinds of applications and can be used not only with airsoft guns but also with other items.

Next, we'll raise the spring height.

Since there are no parts to raise the spring, I'll make a ring out of plastic sheet. I'll make a disc with scissors and then just drill a hole in it with the rotary tool I mentioned above. You can also drill the hole with a vise, but using a rotary tool is overwhelmingly faster and easier.

After adjusting the amount of height increase in various ways, I decided to use two 1mm thick boards to make a total height of 2mm.

I initially tried using three 3mm pieces, but the spring's compression length and the 3mm height prevented the piston from fully retracting, resulting in no engagement with the sear and no operation. While there may be individual differences, I think a 2mm rise is a good guideline.

Tamiya plastic sheet, 1mm thick.
There's no particular reason, but I use Tamiya products because they seem to be readily available and have good precision. Incidentally, the thicknesses I use most often are 0.2mm, 0.5mm, and 1mm.

We will incorporate this.

When assembling, be sure to include the parts shown in the photo and the ejection cover.

Now we'll assemble the exterior parts.

Installation and completion of exterior parts

Finally, we'll assemble the exterior parts.

To improve the movement of the safety mechanism, apply Bellhammer No. 0 Gold Grease to the area shown in the photo.

Next, we'll replace the pin that inserts into the main body to attach the G&P rail.

The location is shown in the following photo.

Next, we'll attach the remaining exterior parts.

It's a rail.

Finally, here's the stock.

By chance, the rail groove and the front sight became iron sights. It was purely coincidental. However, I'm not sure if the aiming point is accurate (the front sight can be rotated, so I think it's accurate left and right, but what about up and down?).

I tried setting it up using the finished product plus some small items I had at home.

It's the other side.

The scope I used for the setup is the Foresta from Vector Optics. If you're interested, I wrote an article about it, so please take a look.

Next, we will check the actual firing performance.

Confirmation of live-fire performance

Finally, we will check the actual firing performance.

The conditions are that the room temperature is approximately 22°C.

The BBs used are VFC Bio BBs 0.2g, and the hop-up is set to the minimum (this is a bit hard to see).

My target was around 0.9J, so this is good.

I fired several shots and took measurements.

It feels a little inconsistent at first, but I think the accuracy will improve as it settles in.

Next, I applied a large amount of hop-up and measured the BBs just before they jammed.

The initial velocity has decreased, so the hop-up is working effectively.

Introduction article on chronographs

Finally, here's a video of it in operation.

I placed the camera at the same distance as in the unboxing video, so I think it can be used to evaluate the sound.

Maruzen CA870 NEW HOP after customization

It's hard to tell from the picture, but the spring noise is gone.

It comes with a supplement.

Maruzen CA870 NEW HOP Custom with Suppressor

It's quite quiet. The cocking sound is more noticeable than the firing sound.

It's straight out of the box.

Maruzen CA870 NEW HOP, straight out of the box

You'll notice that it's quieter when you compare them.

Also, although it's hard to convey in photos and videos, the cocking and trigger feel are incredibly smooth and satisfying.

Regarding the ballistics, I think there shouldn't be any problems since I'm using the original packing, but I'll check later and update this information.

Ballistics confirmation

I went airsofting and checked the trajectory of my modified CA870.

I checked with Yanex.

It's like a microwave.

The conditions were such that the temperature was around 3°C.

The gun itself performed quite well, with a muzzle velocity of 84.5 m/s using 0.25g BBs (measured on-site).

This is a ballistic trajectory image.

Using the iron sights for precise aiming, I was able to hit a frying pan (about 30cm in diameter) at 40m with almost perfect accuracy, and a human-shaped target at 45m was easily hit. If I were to attach a scope and properly zero it, and use the hop-up to create a parabolic trajectory with a slight elevation, I think I could just about hit a man-sized target at 50m (I didn't have time to zero the scope properly, which was a hassle).

I think we achieved quite good accuracy and range.

Using heavier bullets might make it even more interesting.

That concludes the verification.

This is completed.

G&G Bio-Bullets 0.2g
It's inexpensive and accurate, so I use it for a wide range of purposes, from performance testing to airsoft games. It's been my favorite since it first came to Japan (around 2008). It lasts a long time for a biodegradable product.

G&G Bio-Bullets 0.25g
It's 0.25g. I generally use 0.25g BBs when playing airsoft.

Recipe and summary

Finally, here's the recipe.

The performance guideline is a quiet design with a muzzle velocity of 95 m/s or less using 0.2g BBs.

That's it. The rest involves careful assembly, greasing, and any additional machining to finish it off.

Summary

It already has excellent performance right out of the box, but with a little tweaking, it can be made even better.

This type of gun is often used for long-range sniping, but if the muzzle velocity with 0.2g BBs out of the box is under 90m/s (which I think is a self-imposed limit), then heavier BBs used to increase range will be a bit too heavy for this gun. So, I customized it to slightly increase the muzzle velocity, and I think 0.25g BBs are the appropriate weight. Based on the shape and hardness of the hop-up bucking, I think it can handle up to 0.3g BBs (most fields only handle up to 0.28g).

The various movable parts are fine right out of the box, but the customization has improved the feel of each control system.

Even in its stock condition, the spring noise is usually inaudible to anyone but the shooter, but we've managed to reduce it to a level where even the shooter can't hear it.

With added expandability, I think you can create a silent sniper setup using a suppressor and scope.

About Miyagawa Hop Packing and Nonbyne Springs

This time, I decided against using the Hanamaru hop packing, but it seems to have a slightly larger outer diameter compared to the genuine part (this might be due to individual differences).

The packing becomes too cramped inside the chamber, the hop-up protrusion is too large, resulting in hop-up even when the hop-off setting is off, and the nozzle seems to be too thick around the opening, preventing it from fully inserting (I would have preferred to use the hop-up shape if possible).

I purchased a nitrile rubber with a hardness of 60, so I think the situation would be different if I used silicone or a lower hardness, but the 60 hardness I chose this time didn't work well.

Regarding the other part, the Non-Bine Spring 0.9J, from my experience as this is my second time installing it upon request, it does effectively suppress spring noise, but the initial velocity is often not 0.9J, but rather around 90m/s with 0.2g BBs (about 0.85J). If you always aim for 0.9J, you will need to add 2mm of material.

I suspect that applying too much grease might be the cause of this phenomenon. However, considering lubrication performance and durability, I think it's important to apply grease thoroughly.

Thank you for bearing with me through this lengthy explanation.

Maruzen CA870 Charger NEW HOP
This is the product I introduced this time. The old Hop version is almost impossible to find on the market, but the NEW HOP version has a sticker on the box, so please be careful when purchasing.

From here on, the basic structure is the same, only the exterior is different, so the same customizations should be possible.

Maruzen CA870 Stock
I personally prefer the curved stock style, the traditional style.

Maruzen CA870 Sawed-off
This is the lightest and most compact type. I think it's suitable for those who like to charge in aggressively. Personally, I find it easier to cock with a stock.

Maruzen CA870 Bulldog
This model is lightweight, compact, and features a grip on the fore-end for improved rapid-fire capabilities. It might be the most suitable model for airsoft games.

G&P M870 shotgun shell loading port style magazine, 22 rounds capacity.
Personally, I think it looks cool to put this magazine on a CA870 stock to give it an M870-like appearance. The magazine capacity is reduced, but it still has 22 rounds, so I don't think it's a problem.