SKU: 30056332458

Polarstar Kythera SA (Semi Auto) - M4 Version

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Description

Polarstar Kythera SA (Semi Auto) - M4 VersionThe Kythera has been the most eagerly anticipated products from PolarStar in the past decade. This HPA system is a radical departure from all previous systems that PolarStar has produced since the Kythera does not use a battery, an FCU or any type of electronics. The Kythera is completely mechanical. This means you never have to worry about charging batteries or work with delicate electronics. It also means that the system is completely waterproof.

The Kythera has been the most eagerly anticipated products from PolarStar in the past decade. This HPA system is a radical departure from all previous systems that PolarStar has produced since the Kythera does not use a battery, an FCU or any type of electronics. The Kythera is completely mechanical. This means you never have to worry about charging batteries or work with delicate electronics. It also means that the system is completely waterproof.

The name "Kythera" (ky-the-ra) was derived from the Antikythera Mechanism which is a mysterious device that was discovered by sponge divers off the coast of the Greek island Antikyther. The mechanism was so advanced in design that scientists have been studying it for decades to discover its purpose. The machine dates from around the end of the 2nd century B.C. and is the most sophisticated mechanism known from the ancient world. Nothing as complex is known for the next thousand years. The Antikythera Mechanism is now understood to be dedicated to astronomical phenomena and operates as a complex mechanical "computer" which tracks the cycles of the Solar System.

For this reason we used the name Kythera for the valve mechanism at the core of a new line of PolarStar mechanical HPA systems. Although it contains very few parts and is easy to install and maintain, the system incorporates a very intelligent design and is unlike anything else on the market. The system was designed as a mechanical system from the ground up and uses a realistic trigger mechanism which can be applied to single-shot, semi-automatic and fully-automatic systems.


The first of these systems is Kythera SA (Semi-Automatic), the semi-auto-only variant for use in AEG gearboxes.


So, what makes the Kythera so unique?

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Realistic Trigger

What sets this system apart from other mechanical systems is the design of its trigger. The trigger mechanism is designed to replicate the function, weight and feel of a real single-action firearm trigger. It feels real because it is real. The hardened alloy steel sears catch and release the stainless steel spool valve in the same way the sears of a real firearm catch and release the hammer or striker. This gives the Kythera trigger the distinct break and reset you would expect to feel when firing a real single action firearm. The trigger mechanism in the Kythera SA is also adjustable, allowing the user to fine tune the weight and over travel. Additionally, the internal firing valve is balanced and the only force applied during firing is the main spring. This means the function and feel of the trigger is independent of input pressure and velocity.

Complete Shot Cycle

The design of the Kythera SA completes a shot cycle on the trigger pull. This gives you the proven closed bolt performance of the Fusion Engine and F2 in a completely mechanical, waterproof system with a realistic trigger. It does not require the trigger to be released before the nozzle chambers the next round and the firing volume is refilled. This occurs automatically and consistently every shot, with adjustable nozzle dwell and return speed.

As the system resets and recharges immediately after firing, it is ready to fire again before the trigger has been released. This means the system can cycle very quickly for faster follow up shots and a lower potential for double feeding.

Extremely Efficient and Consistent

The valve design of the Kythera operates without the need for air to control the opening or closing of the valve. Without a pilot valve, 100% of the air going into the system is fired through the nozzle allowing it to operate very efficiently. In addition to being extremely efficient, the system is also extremely consistent. The valve is released at the same point every shot with the same force applied, regardless of trigger input.

Universal Charging Cord

The steel cord visible at the back of the system is attached to a cocking mechanism for the internal spool valve.  Although the system automatically cocks the spool valve when the system is pressurized, since the Kythera uses a balanced valve, it is possible in certain situations that the valve could stall and needs to be manually cocked. This typically only happens if the system is run completely out of air so that the pressure drops below the operating range of the system. The cord is designed to be either routed through the grip of the rifle for easy access or even possibly attached in some fashion to the charging handle.

 

Easy Installation

The Kythera SA system installs into a standard gearbox as a single assembly and typically does not require any modification to the gearbox. There are no separate parts to install and the only parts needing to be retained from the gearbox is the trigger, spring guide, selector and safety components.


Wide Velocity Adjustment Range

The Kythera has a wide operating pressure range of 60psi to 180psi which allows you to fine tune the velocity of the system and tailor for different requirements and applications. Within this pressure range we observed a muzzle velocity of 270 - 500fps w/ .20g using a 6.05x380mm barrel. This lets a single Kythera be used in any role ranging from CQB to Sniper by mainly just adjusting the input pressure from your air rig.


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  • Designed from the ground up as a high performance mechanical HPA system, not a modification of a solenoid operated design.
  • Patent pending valve mechanism provides excellent efficiency and consistent velocity combined with a realistic trigger pull and reset.
  • Completes a full shot cycle on the trigger pull alone which translates into consistent nozzle movement and rapid follow up shots.
  • Adjustable trigger. Adjustments include: Weight, length of pull and over travel.
  • Adjustable nozzle dwell/return speed.
  • Wide operating pressure range of 60 to 180psi.

 

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SKU: 30056332458

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tlgb
Charlottesville, US
★★★★★ 5
solid old style docs construction
i am a medium to wide-ish 7.5 in women's, that typically wears an 8 for room. these fit like a wider, roomy 8.5 women's. that is fine because i intend to wear them with thicker socks and for long walks.they are immediately comfortable, and do not feel like they will have the typical brutal break in period. very stable and fitted around the ankle, yet not impossible to pull on and off. they are so handsome, and meet my expectations.
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Reviewed in the United States on November 11, 2025
A
Verified Purchase
Amazon Customer
Pawtucket, US
★★★★★ 5
Get it!!
Size: 6 Women/5 Men, Color: Black Blizzard Wp
This shoe has been a dream for me. I live in an area that gets snow so having the inner lining is great. My feet haven't been cold and I’ve not felt the need to multi-layer my socks, like with other shoes. Unlike most doc marts, I did nor have to break in this shoe, its been very comfy from the get. Material is really durable and has lasted me a long time. This is a great shoe, especially for how affordable it is.
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Reviewed in the United States on December 31, 2025
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Verified Purchase
Cody
Alexandria, US
★★★★★ 5
Authentic Docs for great price!
The boots I purchased were Chelsea 2976 in Nappa leather (not the brown Crazy Horse, but the Black; such nice and soft leather!) and unisex size men's 7/women's 8/EU 39 (I'm normally a women's US 9/EU 40, but that's what fit best--see notes on sizing below). Considering the price, I was a little skeptical that these were genuinely Dr. Marten's, so I ended up bring them into a store to verify before wearing them--and multiple salespeople, who had worked for the company for 7+ years, said they looked like the real deal to them, which is amazing for the price (I got them when they were $99 online, but $160 in store; may have been a sale...?). Before ordering, I also visited the store to get the right sizing--Dr. Marten's doesn't sell my normal size in the US (EU 40), so I needed help figuring out what to buy. In the end that was either a women's EU 41 or a unisex 39. Dr. Marten's women's sizes are cut more narrow, so if purchasing women's, I needed a longer shoe to give my toes more space (EU 41, which they say is a women's US 9 but on many shoes EU 41 is a US 9.5 or even US 10). Unisex sizes are wider, so I was fine with a shorter length (EU 39). In the end, the only real difference between the women's sizing and men's sizing on the Chelsea boot was at the ankle; for some reason, the women's 41 had more of a gap at the ankle and I worried that might make it rub/blister more, so I went with unisex sizing. It might also depend on the boot, so I'd say go to the store for sizing before purchasing online. Once I got them & verified their authenticity, I got a but of things to help with weatherizing them and breaking them in (Dr. Marten's has a great kit! And, double thick socks). I did get a bad blister wearing them too long & uphill on the first day (and I had to get used to their weight; I don't have many heavier shoes). But, I used Compeed patches for the blister (should have put them on to prevent, but it was fine once they were on) and after a week of wearing them a little bit at a time, they are now super comfortable and I love them! Highly recommend!
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Reviewed in the United States on February 19, 2024
M
Verified Purchase
M
Lowell, US
★★★★★ 5
Function and style
Size: 11 Women/10 Men, Color: Black Blizzard Wp
Ideal boot for the winter, snow, mud, etc. Protect your feet beautifully, stylishly. Tip: Wear with two socks to help break in for the first couple weeks. If you are a half size, round up. This is the model without laces, makes for easy slip on / slip off for those pesky people who insist on having you take off your shoes at their house! Ha ha, you know who you are.
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Reviewed in the United States on April 13, 2026
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Verified Purchase
Michael
Cuba, US
★★★★★ 4
Size up for a little bit of heel slip
Size: 9 Women/8 Men, Color: Black Nappa
It’s still a doc and the air sole with bottom out kinda quick but it’s comfortable at first. Size up for a little bit of heel slip so you don’t get heel blisters but not too big of a size jump. Think of it kind of like a cowboy boot size
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Reviewed in the United States on December 30, 2025

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