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ICS Bolt Cover Spring

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Free Shipping on Orders $200 or More ($9.99 for orders under $200)

Fox Airsoft offers a 30 day warranty and return policy.

About the ICS Bolt Cover Spring

This is a replacement bolt cover spring for any ICS M4 AEGs with the simulated blowback function. Your blowback mechanism cannot function without this. This will not work on non-blowback ICS guns as you cannot convert them. This is not a wear item and does not need to be replaced regularly. In all honesty most of the time people will need to purchase this is to build a spare UK1 upper gearbox or they lost this component when taking the gearbox apart. No worries! We got you!

About the ICS UK1 Gearboxes

Starting with the TransforM4 series, ICS upgraded their airsoft guns utilizing the split gearbox design to now include a simulated blowback function. The blowback function was driven by the special piston installed in these gearboxes which have a notch that pulls an external arm connected to the fake bolt cover. The spring provides the springiness in the bolt cover so whether the piston was fully forward or not, you could still pull the charging handle to move the fake bolt and still access your hopup. This feature is now standard among any of the proline ICS rifles which include the MMR, CXP, and the updated TransforM4 series. 

The great thing about this feature on any of the ICS proline guns is this feature does not take away from the performance of the gun. By design with some other manufacturers, the simulated blowback may come from a mechanical arm attached to the piston that does not reciprocate creating more mass to move when the motor and gearbox and put under load. This has been proven to be very inefficient and leads to other problems when the gun does not cycle smoothly. Other designs that were not good were ones that took some of the air pressure out of the gearbox and diverted some of it to drive a fake bolt. This lead to wildly fluctuating fps (velocity) when the guns performance was starting to degrade which made it harder for techs to isolate the problem.

Now on to the rest of the gearbox, some of which you may already know about. The UK1 series gearboxes is an upgrade over their previous models to include a simulated blowback. All the other key features are still there. The split gearbox allows you to perform maintenance, repairs, and upgrades with ease by isolating the components to either the top half of the gearbox or lower half. This allows you to service the gun without a full teardown as well as identify problems without having to explore the gearbox in pieces. Some incremental changes to the gearbox have occurred over time with additions including a quick change spring guide which makes upgrading or downgrading your ICS take less than 30 seconds (instead of the half hour to hour of a traditional gearbox!

Quick Look: 

  • OEM Replacement bolt cover spring

What's Included:

  • Bolt cover spring
  • Metal washer


  • TransforM4 series
  • MMR series
  • CXP series
  • Any UK1-type gearboxes

Alternate Lookup: 

  • NA-214

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— R. King
Awesome company and products. Received sooner than projected from Colorado and I'm in California. Less than 2 days from placing order to receiving it. . Everything shipped as ordered . Incredible selection and great price... Did my homework and eventually came back to them. I'm glad I did. My squad will be ordering and I be ordering more gear as well.
— John
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— Matt
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