M4 Upgrade Path

20 07 2007

I bought my Classic Army M4 with the intent of keeping it stock, but I should have known better. I loved the performance of the gun when I first got it home and shot it in the back yard. The rate of fire was decent, and the fps was a marked improvement over my UTG MP5. While I loved the performance, I’ve always been the type to look for anyway to improve something… and then make it better. Needless to say, I upgraded the barrel to a Madbull 6.03 Aluminum Inner Barrel and then added the Madbull Shark Hop-up unit. I was pretty pleased. The consistency is great, and the gun reliable.

Then I went to play a skirmish as a local field. I was getting hosed and out ranged by a slew of other AEG’s. I’ve chrono’d my M4 @ 320-325 feet per second, these guys are shooting closer to 400 fps. Suddenly I’m not pleased. So much for keeping this gun stock. My current plan it to upgrade to as close to 400 fps as I can get without going over and retain a decent ROF (rate of fire). I took a look at the stock gearbox (from the outside) and pleasantly found that the gun has 7mm bearings, so keeping a decent ROF shouldn’t be too hard. I recently got my hands on a 9.6 volt battery and tried it out for the first time in this AEG and was wowed. The difference in trigger response and ROF is intense. Here is my proposed upgrade path (some of which has already been completed):

  1. Upgraded Hop Up Rubber (Madbull Shark w/Fishbone)
  2. Madbull 6.03 363mm inner barrel
  3. Element Silent Piston head and cylinder head
  4. Madbull Piston
  5. Madbull Spring (M120)
  6. Bearing Spring Guide (undecided if this is necessary)

Okay, so 1 and 2 are done. The gun is consistent and range is decent, but a bit more fps might help as the Madbull hop up rubber (black) is a bit stiff and works better at higher fps. The choice of the Element Silent Piston head and cylinder head was based on price and function. I can pick it up pretty cheap and I am going for anything that might keep this thing a touch quieter. The Madbull piston was donated by Madbull for review (but I didn’t have a piston head at the time to try it out with). The stock piston is showing some stress and part of the rail has a chunk missing so it needs replacing.

As far as the spring goes, I thought I’d try something different. Madbull recently came out with a line of AEG springs and I figured I’d be one of the guinea pigs and try one out. I looked everywhere and, even though AirsoftGI had them a few weeks ago, I can’t find them anywhere now. I contacted Madbull and JAG Precision and they donated one to me for the purpose of upgrading my gun and I’m sure they don’t mind having me talk about it here! So… mad props to Madbull. Soon I’m going to have to stick Madbull stickers on my AEG and mark it up like a NASCAR vehicle! Those stickers add fps right?


Now I’m down to the spring guide. This is a point of contention for me. On a previous gun I chose to install a Systema Bearing Spring Guide, but mainly because I didn’t know what kind of quality to expect from the gearbox and wanted to reduce stress as much as possible. This time around, I’m working with a Classic Army gearbox that is solid and comes stock with a metal spring guide. I’m not concerned about anything breaking, but the bearing spring guide might help reduce stress on the spring and piston head, therefore increase the life of those parts. So I’m torn. I’d gladly accept input from you guys (there is a comment button down there you know!).

So that’s the path I’m taking. I figure I’ll be able to hit near 400 fps, and be pushing about the stock ROF (by upgrading to the 9.6v battery). I’ll chrono the gun afterwards and let you all know how well it’s working and continue to fill you in on the quality of the upgrades and how they are holding up.





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