JM Gen 9 Spring Retainer / Gearbox Case

Just finished reassembling a Gen 9 M4A1, first time working on one. It has a black nylon gearbox, not the earlier clear version.

The gearbox case seems to be a pretty flimsy offering with a dodgy spring retaining setup. I want to experiment with different piston spring upgrades, but I don’t have a lot of confidence in the strength of the gearbox case, even with a moderate upgrade to 1.3mm

Is the box strong enough for heavier springs or is there a way to strengthen the setup that’s there?

i got one of those ebay magxxxxx whatever matel 1.2 spring in my ACR with stock spring retainer.
about 10-15 mag run time now, seems fine, nothing crack so far O_O
but that’s mainly with 7.4 and single shot mode, i don’t really use full auto much,
so there is less stress on the box i would assume.

but i doubt the nylon gears and stock motor will like 1.3 (or over) much tho?
also from memory Rattler mentioned using light weight piston / piston head, will help a bit with lowering hammer force to reduce a bit of stress?

Compared to the old Gen 8 gearboxes these Gen 9 ones are pretty crappy. :thinking: More fiddly to assemble as well.

Just goes to show that each successive generation of blaster is not necessarily an improvement… I think the Gen 9 M4A1s are a huge improvement build wise over the Gen 8s, but not in every aspect… just my opinion.

I run a 1.3 in one of my acr with a 3s 11v lipo,
It’s done a heap of games and few back yard skirmishes. No problem
The nylon gearbox and gears are better than you think

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Odd question and off topic but do u know if gen8 lower receiver fit gen9 upper o.O?
With gen8 box ofcoz

Gen 8 M4A1s don’t have an upper and lower receiver like the Gen 9s. They’re two piece split down the middle.

That split receiver look moulded into the case halves is just cosmetic.

Are you thinking of a Gen 8 box in a Gen 9 receiver? :thinking:

I have to say that the Gen 9 teardown’s very easy if you just want to access the top of the receiver, and that floating t piece arrangement is great for barrel swaps. Don’t even have to take your hop up off to remove the whole upper receiver. :+1:

Shame you have to completely remove the buffer tube, hand grip, motor and lower receiver to do a simple spring change though… :thinking:

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Arh that sux :frowning:
Nah I was thinking how gen8 hanfguard and buttstock mount are very different to standard so wondering if the top half can be swapped

Nope… there is no top half… just a left and right. :wink:

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