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Discussion Starter · #1 ·
My G&G cm 16 raider L is getting a cheap cyma gearbox to get it up and running while I figure out what I want. This thing sitting on the table in my basement gave me a thought when I started watching some YouTube videos.
why not build a frankengun?
M4 parts should be mostly compatible and considering the frequency at which people upgrade this or that it seems like they almost all end up custom anyway.
from what I gather this far, the upper and lower receiver really need to match, then find a gearbox shell that fits the receiver and go from there.
looking at the parts suggested for my G&G I feel like I could build something for maybe $200 or so that would out perform some of the $500 guns on the market. Am I missing something here or is that basically true.
I was going to start by seeing if I can get a good metal upper/lower combo, maybe something With broken internals and whatnot.
I may buy a fully assembled gearbox because looking at mine in pieces, shimming and messing with those tiny parts and springs are not something my beat to death hands will be able to do. Or, alternatively, pay a tech on here to build me a gearbox.
Am I on the right track or am I missing something here?
 

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How technically inclined are you? I would personally suggest avoiding techs, since it’s actually kinda rare to find folks who really know what they’re doing. I was on the field Saturday, and started talking to this guy, who shows me his $1500 custom VFC build. I went to flip the selector to semi… and the tech had left out some DIY mods for the selector sticker to work on the optical ETU. The gun was also pretty badly shimmed—sounded significantly worse than my bone stock Arcturus.

M4 parts are… kinda compatible. Ambi bolt catches and fire selectors are typically your enemy. Some gearboxes are also different thicknesses, so sometimes you have to be careful with what motor grip you’re using. Other folks know more than I do.

If you have a bone stock G&G CM-16, you can probably spend under $100 to make it outperform Krytacs and VFCs and the other $500 stock guns. You can spend $200 and go for some nice features as well, like a Perun Hybrid or GATE Aster or whatnot.

If you’re trying to get a higher rate of fire/better trigger response balanced with better effective range, I’d go:

$30 40K motor (available from Aliexpress)

Stock gears

If the piston isn’t full metal rack already, I’d go SHS. Get the $12 piston and head combo off Amazon if the PH isn’t giving a good seal.

Keep the rest of the GB stock, aside from proper shimming, AOE correction if needed, and other small DIY tweaks.

$5 Stock Krytac barrel from Umbrella Armory if yours looks scratched up or warped. If not, polish the barrel nicely.

Right now, I have to say, the PDI W-hold 50 degree is my favorite hop rubber: $10

$15 plug in Mosfet that attaches to your battery cable, or make your own if you can solder well.

$20 quality 11.1v lipo

Spend whatever you have left on a charger for that lipo, if you don’t have a charger already.

This is assuming that all the other parts are in good condition. :)
 

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Discussion Starter · #3 ·
How technically inclined are you? I would personally suggest avoiding techs, since it’s actually kinda rare to find folks who really know what they’re doing. I was on the field Saturday, and started talking to this guy, who shows me his $1500 custom VFC build. I went to flip the selector to semi… and the tech had left out some DIY mods for the selector sticker to work on the optical ETU. The gun was also pretty badly shimmed—sounded significantly worse than my bone stock Arcturus.

M4 parts are… kinda compatible. Ambi bolt catches and fire selectors are typically your enemy. Some gearboxes are also different thicknesses, so sometimes you have to be careful with what motor grip you’re using. Other folks know more than I do.

If you have a bone stock G&G CM-16, you can probably spend under $100 to make it outperform Krytacs and VFCs and the other $500 stock guns. You can spend $200 and go for some nice features as well, like a Perun Hybrid or GATE Aster or whatnot.

If you’re trying to get a higher rate of fire/better trigger response balanced with better effective range, I’d go:

$30 40K motor (available from Aliexpress)

Stock gears

If the piston isn’t full metal rack already, I’d go SHS. Get the $12 piston and head combo off Amazon if the PH isn’t giving a good seal.

Keep the rest of the GB stock, aside from proper shimming, AOE correction if needed, and other small DIY tweaks.

$5 Stock Krytac barrel from Umbrella Armory if yours looks scratched up or warped. If not, polish the barrel nicely.

Right now, I have to say, the PDI W-hold 50 degree is my favorite hop rubber: $10

$15 plug in Mosfet that attaches to your battery cable, or make your own if you can solder well.

$20 quality 11.1v lipo

Spend whatever you have left on a charger for that lipo, if you don’t have a charger already.

This is assuming that all the other parts are in good condition. :)
I'm not going to mess around with the gearbox internals myself even shimming. I pulled the original apart and there's no way my caveman hands are getting some of those tiny springs back in place plust I have enough nerve damage that it would just be too frustrating to bother. It's Just not happening. So for the gearbox, I'd either have one upgraded by whereever i buy it or just buy a really good one with a Mosfet already in it. I know some retailers offer some of that stuff for the gear boxes.

I'm not too concerned with ROF. More accuracy and range bordering on the performance of a good DMR.

As for the G&G body..I have the gen 1. It's ok but not the look i ultimately want. I just ordered a cheap Cyma gearbox for it with a motor for like $75 for both just to get it running. Next I'll get a barrel and and hop rubber but thats about it for that gun and I'll start working on building something really nice from the ground up.

Good to know about those parts you mentioned cause they're going to be my starting point.
 

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75% of your accuracy comes from your barrel group: hop up unit, packing/bucking, nub and barrel. There is a vast array of combinations for this and takes some trial and error to get right.

10% comes from the weight and quality of ammo you are using. You'll need to play around with this one as different weights will perform differently.

10% comes from how consistently your gun shoots shot-to-shot. Keeping fps deviation to a minimum is key here. This takes some tuning.

5% comes from Mother Nature as she either blesses your shots or curses them :) All luck and no skill here.

The Gen1 Combat Machines are fairly receptive to upgrades and the such. Just know that nothing is made to any standard and you will run into fitment issues at some point.
 

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M4 parts should be mostly compatible
My CQB primary is a ~2008 UTG Sport model 4, perhaps sharing some notes on the various little odd things I learned while building it and others would be valuable here - only the upper and lower receiver on this gun are original at this point, everything else has broken and been replaced over the past however may years. I've got over 1k in it in parts last I added it all up and it's the sweetest little gun to shoot... Here's some things I've encountered which I wouldn't have considered beforehand.

The disk on the back of the selector switch (the part that interfaces with the selector plate) was a smaller diameter on the UTG than others which caused the gun to be really finicky when switching from semi to AUTO in some configurations. I also learned that some are thicker than others as well, chased that issue around and around until finally finding a lonex switch set that fit the receiver and was the right size to interface with my gearbox of choice (also Lonex at that point, go figure).

The trigger pin in the original gun was a hair thicker than in several aftermarket gearboxes I've had in it over the years, had to either bore/ream the gearbox or run a thinner pin. Did both at different points, currently bored out which means the gearbox will be loose in any other receiver / cannot leave this gun until it breaks.

I had issues with a few gearboxes where the back / where the bolt from the stock goes into the gearbox is shaped differently between OEMs, some shells sit nicely in the lower and some tilt back when the stock is tightened. I eventually drilled the back of the receiver out and tapped threads for a large grub screw with a hole through the middle which allows me to adjust the angle of the gearbox as needed. This is a great solution, but holy heck is it important to get that hole tapped straight.

Triggers are always a issue if you don't use a stock curved style, and sometimes even if you do - I've filed a good 5mm off the front of the cutout in this gun to make room for a dozen or so different bang-switches. Trigger guards, I like the 'enhhanced' version with a slight curve to the bottom as it keeps my hands from slipping forward when working corners - turns out there's a number of different widths there as well and that's a spec that is extremely rare to find listed.

Magazine releases are tricky, some are interchangeable and some just aren't due to being slightly to thick, to long, etc. Got lucky and a Lonex one again fit this receiver's cutout perfectly, but even there the ramp was to steep and it made loading mags feel really chunky. Fixed it by filing it way down, gave it a much more gradual angle.

Finding the right nozzle length can be a pain when things are mismatched, past solution was to get a polymer unit and use a special bevel-bit (works like a traditional pencil sharpener) for my dremel to custom fit it. Fortunately the Maxx chamber I'm using now hasn't given me any real trouble, pairs really well with the receiver and gearbox.

Outer barrels, need to keep an eye on the backspacing, the rim or the 'lip', and hop chamber cutout. Some 'lips' are thinner than others so when the nut is fully tight, the barrel is still loose - shims on the front of the barrel will fix this. Sometimes the backspacing is wrong and the outer barrel actually extends into the upper receiver a bit; there are special shims to fix this but they are few and far between these days if you're looking. I'll post a pic if anyone is interested, pretty obscure. Hop chamber cutouts are a mess - some are deep, some shallow, some wide, some tight... and naturally differnt hop chambers are longer, shorter, wider, etc etc as well. Finding a good fit can drive you mad lol. Also (and I assume you know this, but just to cover it) airsoft upper receiver threads for the barrel nut are not all made equal- some are actually mil spec, some are 'airsoft spec' which is smaller iirc, and some are just sloppy cast threads that it's hard to get anything to grab on. As a result, odds of one handguard fitting another upper is 50/50 at best.

Rail height over bore is also highly variable between OEMs, meaning the top rail on the receiver isn't always going to be level with that on your handguard if you want the flat top look while mixing and matching. Some are good, some are close, and some are 1mm higher (or lower) and just look terrible.

Motor grips are occasionally different. This is slightly less common to see now that many guns come from the same factory, but the cutout in the receiver that the grip goes into can be longer, shorter, taller, etc. Different gearboxes can also be a bit longer or shorter here too, resulting in a ugly gap around your grip or the grip not quite fitting - or even worse, appearing to fit but the motor angle is all messed up.

Charging handles are usually somewhat proprietary, have had very little luck swapping between OEMs on any of my guns.

Dust covers, there's 3-4 different latch styles and some variation on tab length as well. Have to pay really close attention when selecting one for a different upper, odd's are high it wont fit. Should also mention, the dust cover pin can be different diameters and there's a couple different ways they are mounted too - most use a c clip, but the size of that clip is also different.

Takdown pins! omfg, takedown pins. Every OEM seems to use a little different style, length, etc. If you have to replace the original ones for whatever reason I've had the best luck with locking pins as they are by nature somewhat more forgiving if the length isn't perfect - but even then I usually have to sand them down for mixed builds. King Arms pins aren't always the right length for King Arms receivers, etc etc.

So yeah. All M4's are basically the same, but the size of the asterisk next to that statement is freaking yuge when you really dig into it and start trying to fit parts together. You're going to find this a very frustrating process at times, but if you push through it, if you remain committed to the build... In the end, it's worth it. Might not look like much to anyone else, might just seem like any other black m4, but to you - it'll shine.

Here's the gun I referenced btw. Currently 16:1 1j DSG, 21t, ~48rps on a smol buffer tube stick
Air gun Trigger Gun barrel Gun accessory Airsoft gun


And this is how it was ~15 years ago, 18:1 1j SSG, 28tpa, ~12rps on a 8.4v NiMH boat anchor
Trigger Air gun Gun barrel Machine gun Gas

Not the same gun, but same model and year - also mine :)
 

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Discussion Starter · #9 ·
So, Ive purchased a new gearbox and hopup. The gearbox is one of the combo's on Evike made by Cyma that comes with a motor and the hopup is a lancer tactical rotary thats machined and not one of the plastic ones.

I did notice my inner barrel isnt straight, theres a sub 1 mm curvature along the length and I'll be replacing that in 2 weeks. I found a well stocked shop near me and the tech there was saying to go with a 6.02 or 6.01 barrel if I'm looking for range and accuracy.

So my questions are:
1. IS there any benefit with a 6.01 or 6.02 over a 6.03 on amazon or with a cheap gearbox is it a waste?
2. How bad will the slight curve be if I just want to get out on the field next week when my gun is working again.

I figure I'll do the barrel and leave the gun as is after that and really decide what to get for a new gun and use this one as my backup if something fails or breaks.
Any thoughts are appreciated.
 

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I’ve had good results with good quality 6.02s, but imo the best bang for your buck is to get a good 6.05mm stock barrel from G&P or Krytac and polish it up. Easily as good as most of those “upgrade” barrels, and since a lot of the “upgrade” barrels have issues they’re just plain better, and you can probably get one for quite a bit cheaper, especially if you get a Krytac barrel off Umbrella Armory.

If you do want to get a steel barrel though, for cheap go ZCI, if you feel like spending more skip to a Lambda.

The main difference a tighter barrel gives is a higher FPS. Folks can argue until the end of time over whether a wide bore or tighter bore is better, but in my experience as long as it’s between 6.08 and 6.02 and you do everything else correctly you’ll have a gun that is easily accurate enough for an assault weapon. I’ve bad good results on both ends of the spectrum, though I have to say, for DMR/precision builds where I’m going to be using heavy BBs, 6.05-6.08 is king. In my experience.

Cheaper GB has nothing to do with accuracy—make sure your compression is good, your nozzle doesn’t wobble, nothing drags, and the tappet isn’t weird and everything else is in your barrel group. The only issue could be nozzle fitment, but as far as I know CYMA is fairly tolerant in how their crap works with other folks’ crap.

Also, just a note, you can do practically every single compression fix in the book without needing new parts. It’s almost entirely modding and DIY style fixes.
 

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Discussion Starter · #13 ·
I suppose but it would stick out into the flash hider. Technically the stock barrel is 357 mm and it runs right to the end of the outer barrel where the flash hider begins. I’m not sure I want to buy a mock suppressor at this point and although I could probably remove the excess with a hack saw, I’m unsure about beveling the inside of the barrel. Also with shipping it’s the same price at the on from Amazon…which is an Evike 6.05 brass barrel for 17.95
 
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