ICS M4 – Splitting It in Half

If you have been following the GITV Blog then you’ll know that I have just mentioned how the great company ICS has improved over the years. I have also mentioned that ICS is the original company that created a split gearbox design for their M4 AEG Series. Like I have said before, the public has a love-hate relationship with the split gearbox design. People who own it loved it and people who do not hate it. Well, this article is dedicated to admire the beauty of the ICS M4, and I am going to turn the gun inside out and show you how amazing this split gearbox design really is.

First Impression

When I first picked up one of the M4’s from ICS, I immediately noticed the beauty of the craftsmanship this rifle has. The lower and upper receiver is made of metal. Depending on the model, some ICS M4’s come with RIS units or standard plastic hand guards. The entire gun is extremely solid, there is no wobble of any kind. Just like other full metal M4s, the ICS Full Metal M4 is heavier than my AR-15. Most of the ICS M4 has a standard 14.5” outer barrel and a 363mm inner barrel; therefore, they are ideal for both indoor and outdoor play. The only short coming I see on the ICS M4 is the receiver pin is not retained. I have lost receiver pins before and believe me, it is not fun.

Detailed Inspection


The ICS Full Metal M4 has a standard metal receiver. The one in the photo features a folding stock, which is a nice feature if the operator needs to go into a really confined space such as vehicles. The metal carrying handle can be removed to expose the 1913 picatinny rail and mount optics on to it.  A unique feature of the ICS M4 that you might not be aware of is the forward assist button, on the right side of the upper receiver, functioning as a spring release. ICS is the company that invented this awesome idea, which can prolong the life of the spring.

The RIS unit on this particular ICS M4 is quite unique. It has 2 special screws on the bottom to hold the RIS unit in place. The screws also prevent wobbliness on the gun. The RIS unit contains 4 rails, which is pretty standard. However, I do not like this particular rail due to the fact that it is very wide, it’s awkward just to hold. Continuing to the front, this ICS M4 has a standard triangle front sight post, which can be adjusted for elevation.


The unique feature on all ICS M4s is the split gearbox design. To check out this feature, punch out the rear receiver pin. The top receiver will pivot on the front pin and expose the internals. The lower gear box exposes the gears and the trigger mechanism. After talking to our tech department, this split gear box design has a huge advantage when it comes to maintenance and upgrades. One of the tech stated that shimming the gears on ICS split gear boxes really helped him to shim guns the right way. He can monitor all the gears movement and he can make the most precise shimming.

Not only is shimming easier, changing out stripped piston and changing springs is just as easy. Since the tech is only dealing half a gear box, they have fewer things to worry about. To change a spring or stripped piston, all the tech needs to do is punch out the rear take down pin, and slide the upper gearbox out after splitting open the receivers. The Tech works on half of the gearbox at a time compared to the tradition gearboxes which take much more time to remove from the body.

The ICS M4 uses its own unique hop up unit. With the split gearbox designs, it is easy to work on the hop up unit. After sliding the top gear box out, the inner barrel and the hop up assembly slide out of the upper receiver. One thing our technician told me is that the spring pushing the hop up unit against the air nozzle for a better air seal. However, over time the spring will loose tension, which causes potential air leaks. Air leaks equate to loss of FPS, therefore, keep an eye out for the spring tension.

Overall, this ICS M4 is superb in my book. The ICS M4 is well built externally and it has a genius design for internal. Shooting about 380 FPS right out of the box, this ICS M4 is perfect to skirmish in any outdoor arenas. Pricing at $330, this gun might seem a little bit expensive, but I assure you that this gun is worth every penny. That’s it for now, I am Andrew, stay safe, and get out and play airsoft.

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