Gearbox help please

Hi, can anyone tell me the difference in these 2 gearboxes, and if they’re an easy replacement for the standard v2 in the gen1 m4?

I have put one of the nylon case with nylon gear mrt gearboxes into my old wells with the clear receiver. I just bought the gearbox with no motor for $50 from M4A1 (not shown on website). The version you are looking at appears to have metal gears. Not sure if the head/nozzle and piston are different.
Gearbox went in easily and you can use the new or old t-piece(may need to cut the lower receiver for the new one) . If you use the new t-piece it is a bit of a pain to put the barrel back on because the t-piece hangs down a lot lower into the mag well. I found it goes on easier if you reach up into the mag well and pull the tappet plate back to retract the nozzle while you slide the barrel on. Or just cut a piece out of the front of the receiver so the barrel slides back without fouling on the air nozzle.

Just be careful as the nozzle on the new mrt gearbox has a spacer behind the silicone tip. I think you need this if using the new t-piece. So if you install an upgraded head and nozzle you may need to re-use that spacer. Guys at M4A1 should be able to sort you out.

Haven’t used the black alloy gearbox but think that’s what’s in the wells v4 so should fit fine.

The guys at m4a1 tell me the only difference between them is the nozzle, and both will drop straight in. Doesn’t make sense why there’s a $50 price difference if a $5 part is the only difference haha

Actually the CQB/MRT gearbox is way better value because it has metal cylinder head and nozzle


Ahh see i knew there had to be other differences. I find it strange that the cqb has the 18:1 gear ratio though, ive never had anything to do with cqb but i always thought they ran the 13:1 gears

I’ve never seen an off the shelf with anything other than 18:1
High rof is something we create it’s not mandatory, have you seen any real commonly used CQB weapons with such high rof ?

Ahh yeah makes sense haha. I’m now in 2 minds wether to get one of these gearboxes for my m4 or just get a wells cqb blaster for the same price.

So I ended up doing both… got the cqb blaster and the metal box for my m4. Put the new gearbox in, was firing like A dream for about 3/4 of a mag and now the gels just gather between the mag and t-piece :man_facepalming:

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Could be a number of things but try looking at the nozzle rubber tip and tappet return spring

Yeah it looks like the nozzle isn’t being pulled back far enough to clear the t-piece