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Airsoft_Mr B

A few upgrades to my CA MP5K + Custom Build

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Hey guys, as you may know my first gun was the CA MP5K PDW. I'm kind of disappointed because honestly, in hindsight, I think I should've gone for an MP5A4 as I actually don't like the look of it!

Now back in October / November 2013 I got a new gun, my M4, and I tried selling my MP5K. Needless to say it isn't sold yet, and honestly it isn't in the best condition aesthetically anyway.

I owe my dad £70 for it because the M4 was intended sort of as a replacement to the MP5 (so he wants to get money back on the M4 purchase)

So my hope is that when I've got a job I will pay him back at least 70 for that, but keep the MP5 and customise it!

This also means I get some valuable tech and maintenance experience I've so far been reluctant to do!


Ok so I'm wanting to re-shim my gearbox (version 3?) and install new bushing or bearings. I'm pretty sure I've seen threads on this before but I can't remember which is supposed to be better.

Also, I don't think this is really the easiest upgrade to start off with as somebody who as never gone inside any of their guns before :| So any help would be appreciated.

Am I correct that re-shimming and adding new bushings / bearings is going to increase the life span and reliability as well as improve the sound of my gun?


I'm looking at the ASG Ultimate Shim set (it's only £3.99) Would I need / is it best to go for either the thin or the thick set?

Bushings / bearings from Patrol Base:

  • ASG Ultimate 7mm BEARINGS
  • ASG Ultimate 8mm BEARINGS
  • ASG Ultimate 6mm BUSHINGS

No idea which of these is best for my gearbox or anything about them at all if I'm honest.


By the way I'm in the process of making a new website at Squarespace, it says I only have a trial period so it runs out in 10 days or something...I don't know if that would mean my website would be then taken down or what but I'm writing up about the custom work I'd like to do on there so take a look if you like. I will get a link soon.


Thanks for your help,

J :)


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Some other guns I used for reference / inspiration (externals)


Unfortunately my website isn't live yet (don't know how much it's going to cost either) so you can't view anything on there.

The first photo is very similar to what I would like except I will keep the PDW stock and I'm going to add an AN/PEQ-15 battery box. Need to decide between an AFG or Tango Down stubby foregrip and KX3 or suppressor.

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Bearings should be better, will probably increase the lifespan and may increase the rate of fire a little. The one on the right with the more minimal RIS looks awesome, especially with that massive silencer :)


I would consider making an MP5 collapsible stock fit and maybe find or make a foregrip that can hold a battery (there must be one in existence). This will keep the overall size down. A PEQ box on an MP5K is going to look massive.

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I've never heard of one, but thanks for the suggestion. Yeah a PEQ would look gigantic, and probably really stupid too :/ But then what options do I have other than re-wiring it to the rear?

Perhaps if I tried fabricating a custom holder for the battery...

I could try to find an sticker set or something to make it look more authentic, and I might just be able to pass it off as some kind of custom MP5K LLM/LAM.


Thanks for the advice on bearings by the way. Honestly I prefer the gun on the left actually, both are very cool though :)

I will probably get a Element Noveske KX3 from airsoftworld because it's more compact than a big barrel extension, and I'm going to get a suppressor on my M4. Also I'm leaning towards getting the Golden Eagle Tango Down Stubby VFG from Patrol Base as opposed to replica AFG (has a pressure pad panel)


Here's a thread I found on a battery-holding foregrip:



EDIT: A battery holding foregrip does exist!



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Lonex/ASG Ultimate Bearings are the shiz. Really reliable,smooth and quiet. Just what you need.


ASG Ultimate parts are really really good,they are re branded Lonex who are probably my favorite aftermarket parts for AEGs.


Go for the thin shim set and buy two packets. It's better to have more precise shimming.


Speaking of shimming,I always recommend starting off with the pinion-bevel shimming and then move on to the spur and sector. All the guides which tell you to shim each gear individually are bullshit. Trial and error is the best method imo. Pinion-bevel is the source of 90% of resistance and screech from a gun so it's the most important area.


Get good quality grease as well,I use moby grease for gears and silicone grease for the cylinder.


no.14 O-rings help air seal a fair bit.


I tend to seal cylinder heads with silicone sealant,for max compression.


Try find an ACM Neodymium magnet high torque motor,like a JG M42(AK JG Blue),Chaoli 22TPA motor(Found in some Dboys guns,you can try find Chaoli motors on fleabay) Some CYMA motors like the one on your M4 could be neodymium too. Chinese motors are horrifically inconsistent however(Not in quality!) With some being sold as neo motors but being ferrous motors,some being mislabeled, some looking like neo ones but being ferrite,etc.. JG are a massive culprit in this regard.

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