Gearbox wells M401

What gearboxes other than the mkv2, (or any other metal gearbox) fits in the wells receiver?
Looking for a nylon gearbox

So, doing some research, and most boxes need the receiver to be modified in some way…
Is their any gearboxes that are a perfect fit?
The mkv2 is the only gearbox I’ve seen with little modification. And an actual picture on what need to be filed down for it.

Just don’t see the reason for a metal gearbox casing.

I’ve been waiting for the community to maybe have a better idea…or new input but

MK2 is it really. As mentioned above, much hacky slashy required for anything else

On the …can’t see a point of a metal box…well…once you get around the cost pineapple, the first time you build it, you will know why.

That said, a decent and I do mean decent nylon box is the tits too but the build is not as nice to do as a metal box…one of those…gotta do it to know it things

Dump the wells…after you spend the time doing the things, you may as well gone a native V2 compliant solution.

Less time, less effort, better outcome and given the cost of a metal box, fewer moneyz

Edit: rattler’s daMan…and I totally forgot about that box. May have been the sticker shock :rofl:


If you are after a nylon box for the wells, you could see if m4a1 sell any of the nylon boxes that come out of the new wells. If you want to go metal go a retro arms or mk box, don’t waste your money on the metal wells box, it is old and needs a lot of work done on it to make it decent, I am on my second one of these as I type this.

Thanks guys so really, mkv2 it is…
Gearbox jammed yesterday…
I noticed a crack in the front of the gearbox a few months ago… decided I would keep on going with it till she dies (was still pumping at least 280fps average still)
but yesterday was the day, went to pull the trigger did a few shots then jammed!

Also another question will the wells metal gearbox kit, fit straight into the mkv2?

hey…don’t forget that one rattler put forth. its specifically for the wells.

i understand a little work is required for the mk2 to fit but not much

Didn’t even notice the link…
Thanks rattler! I’ll see what happens… but we all know what the out come will probably be…
Both gearboxes!!!
One for the m401, and another for whatever lands in my hands next!!

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Keep in mind what @Freeman93 said about the cast gearbox.
I personally have built 2 of them so far and only needed a metal cylinder head and nozzle to make them perform.
They have M90 springs and do appox. 340fps and both have over 30,000 gels through them with no issues with cracking.
These cast metal boxes require careful building and will not put up with piston hammering


So I can only afford one at the moment…
I don’t mind tinkering with gearboxes, I installed the stock wells with the all metal kit with a 1.25 spring.(that’s how the crack came to be and well with all that flexing something gave over time and jammed) so im going with the mkv2 first!
Edit: any one got a list of parts that fit the mkv2?
Makes my day ten times easier!

Your going to have to use all Wells internals and MK has a guide on the web page

Exactly what I wanted to hear! Thanks guys will be ordering one tonight!!!

Read the guide because the wells piston is not suitable :+1:


Cheers mate, I’ll look into it more!

Yep the gearbox rattler linked to seems pretty good, you’ll still need to put a few goodies in it to make it right but it is a solid box at a reasonable price

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What dramas have you had with the wells metal box? Only asking as I’ve got one that seems good! Saying that it’s not pushed to its limits with massive spring or crazy rof, but still punching out pretty hard at around 340fps.

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Mine broke around the anti reverse latch, the metal failed there, it was running a 1.28mm uneven spring, with the replacement metal pin and piston and head replaced to stop it leaking, as it was the stock metal box they sold just before the V4. It was barely getting 200fps before I took it into m4a1 to get all that sorted, died about 1 hour after getting it fixed up, was pushing 285 - 320 fps when I got it back before it failed.

Bugger, hopefully the v4 is all improved, I guess I will see. It’s my go to favourite at the moment. It’s accuracy is awesome with just enough punch. I think all things will have their issues in certain areas.

My friend got the v4, it had everything fixed I need to get my box working decently, the metal box is still the same casted box so can only hope it will survive long enough to make it work the cost.

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Oh now I see what happened, a shop tech worked on it ! I’ve seen it so many times :zipper_mouth_face: