Downgrading a KA m4a1

[H0ppyDragon]

Hello all,
I just ordered a new king arms m4a1 from a canadian retailer. The gun has been upgraded to shoot over 420 fps as per Canadian regulations.

The field I would like to play at does not allow anything over 400 fps. So my question is what spring should I get to reach a fps of around 360-380? Also I would like to downgrade so as not to put undue strain on the gearbox.

[JonsM4]

Spring 100

[H0ppyDragon]

So I just noticed the spring chart. Kinda embarrassed now. Lol oh well.

So looks like a king arms m110 would do the trick.

One last question, is this spring good for the gearbox or should I forgo some fps for a more durable setup?

[JLiang]

Because (usually) guns that are upgraded for import are not re-tuned for the higher-velocity spring, the gearboxes are not designed to take that kind of stress. As such, as with all endeavors regarding upgrading a gearbox without upgrading any other parts, the longevity of the gearbox is decreased.

However, if your gearbox was designed to be able to take a heavy spring, like KWA's 2gX gearboxes, then by all means, go ahead.

General rule (again, general, so not everybody's guns may conform with this) of spring velocities:
M90 = 290-300 FPS (CQB Spring)
M100 = 300-330 FPS (General Spring)
M110 = 330-360 FPS (Field Spring)
M120+ = 380FPS+ (Special Spring)

Again, the above chart is rough, and any 'official' chart would be much better for specific reference. Also remember that different companies' springs and spring designations will differ from one another, so research beforehand is a must.

[Styrak]

The above ratings are not some of voodoo either, M100 just means 100 meters/second which translates to 328 feet/second, just FYI.

[JLiang]

Oh, apologies. I was using the following
http://www.airsoftcanada.com/SpringChart.php
and it seemed to point towards the above info. Woops.

[Styrak]

It's true some companies have wacky naming systems, like Guarder's SP100 (really you'd think that was 100m/s but it's not), is 387fps which translates to 120 m/s (really 118 but I rounded up) which is strange.

[JLiang]

I haven't intently researched springs in general, but yes, I can say with confidence that some companies are messed up that way.

[JonsM4]

http://www.airsoftcanada.com/SpringChart.php

[H0ppyDragon]

Ok so after doing a bit of research it seems like this gun should be shooting somewhere around 320 fps stock. So in that case looks like I'll be going with a m100 spring as that would be close to original. And what the stock gearbox can handle.

[8thArmy]

KA internals r pretty sturdy, you'd be running fine up to 400 fps with stock gearbox just FYI

[Smartass]

This is a very timely thread for me. Waiting for delivery of my KA m1a1 from Halifax Airsoft Wholesale any day now. Thanks for all the info.

[MaciekA]

Originally Posted by JLiang

Because (usually) guns that are upgraded for import are not re-tuned for the higher-velocity spring, the gearboxes are not designed to take that kind of stress.

Note, my experience with gearbox in the KA M4A1 suggests that it can very likely happily fire at 420fps until the cows come home... so:

To continue at 420fps (just for fun...):

- Swap the motor for a high torque motor (the stock KA motor has weak magnets),
- Rewire to Deans and install MOSFET (so you can use a more powerful battery to push this spring)
- The stock shimming in this gun is excellent, but the KA M4A1 gearbox I opened was still able to accept a couple of 0.1mm shims.
- Replace hopup bucking with something that can handle >400fps
- Use a juicy LiPo (this point was added to ONLY see if ThunderCactus is reading the thread )
- Check the piston o-ring and possibly swap it for one with a better seal. The stock one kinda sucked even after stretching with a flame.

That's all I'd do. This gun is very close to a perfect stock gun.