Version 2 gearbox - M4/16 vs MP5

[LegioXIII]

I have a question about version 2 gearboxes. Now I know that the M4/M16 and MP5 guns use V2 gearboxes.

What I would like to know is:

Would THIS - King Arms M120 V2 Complete Gearbox - M16A2 - Rear - work for an MP5 if I swapped the selector plate and air nozzle for ones used in the MP5? From what I can tell those are the only things that are different between the two.

I know I can buy all the parts and build and entire mechbox myself, but I'm not feeling that ambitious and would prefer to use a pre-built, drop-in mechbox.

[m102404]

Buying a quality prebuilt is a good way to go. Especially if you don't have anything worthwhile to salvage already.

Here's some things that are model specific though (otherwise the parts are the same between the M16/MP5 mechboxes).

1. Cylinder. The M16 will be a full cylinder...the MP5 a ported cylinder. There are some great articles done up about matching cylinder porting to barrel length (MadMax)....but in short, you'll need to match things up.

2. Nozzle. You've figured this out already.

3. Selector plate. The M-series and MP5 series are different shapes

4. Trigger+trigger spring. The trigger is obvious...the trigger spring shape are usually different (not actually sure why...but the MP5 trigger springs tend to be a lot more bent than the M4/M16). As long as it isn't binding...and returns the trigger...you're g2g

5. Wiring. If your MP5 is a full stock, then no problems...if it isn't then the trailing end of the rear wired M-series wiring harness will not be the right length for your front-battery MP5. Not a big deal...just measure it up, clip the wiring and put on a new plug.

That should be it.

Finally...it'll be up to you to put $200 into the gun. If it's a crappy Mp5 to begin with...you're probably dumping in about 100% of the cost of the gun...and you're still left with a so-so hopup unit, barrel, motor. Whether it's worth it or not is totally up to you.

[ILLusion]

All Armalite v2 gearbox shells can fit in to MP5's, but not vice versa if you're using a gen 2 Tokyo Marui plastic receiver. It's been a long time since I've seen one of these, so chances are, you won't have a problem with it. The only difference, is that Tokyo Marui receivers could split apart for "quick takedown", and had tabs that the rear takedown pin held in place. The gearbox required slots to be cut out around the spring guide area to allow clearance for these rear tabs to pass.

Beyond that, as m102404 said above, a complete M16 gearbox should work, as long as you swap the loading nozzle, selector plate, and trigger to an MP5 counterpart, and also make sure the cylinder matches your inner barrel length as well as wiring matches what you need.

[LegioXIII]

Thanks for the responses. I was toying with the idea of putting together an MP5 because I have enough parts left over from other stuff that it wouldn't take too much to make an entirely "new" gun.

As for spending money vs putting it towards just getting something new - to me, ending up with a new gun was only part of the equation. What I value more is the experience I'd get from playing around, getting parts together, and seeing how everything works. I like the sense of accomplishment from working on things myself.

It's kind of like a long time ago when I knew nothing about computers. I set a challenge for myself, read up as much as I could about the various parts, bought the parts, and put together a relatively decent (for the time) desktop system.

Anyways, I think I'll just let this idea sit for now, but again, thanks for sharing your experience.