Custom airsoft project - internals

[Devellis96]

I'm relatively new to airsoft. When I bought my first gun I didn't pay much (if any) attention to the internals. I currently own a G&G M4. I'm trying to design and build a custom airsoft gun (theme to be disclosed later in the project).

I want to have a burst-fire option and I feel this would be easier to implement with an AEG than a gas, but it would be really cool to have blowback. For now, I'm just looking for advice on AEG internals.
It's going to be bull-pup and optimized for medium-long range.

According to the research I've done so far, I'll need:

-gearbox
-motor
-selector plate
-trigger
-barrel (length ~600mm)
-hop up

1) Am I missing anything?
2) Do you have a favourite model of any of the above components?
3) how does the motor choice affect my battery choice? (I'm going for 900 RPM, not even sure if this is particularly low or high)

Keep in mind, I'm going for a bullpup design which makes things slightly more complicated.

NOTE: Yes I've heard of the search tool. Asking other humans about their experiences is a form of research too.

EDIT: material recommendations? I'm probably going to go with ABS, but I want to hear your opinions

EDIT: I'm designing the externals from scratch (it's going to be bullpup). I'm also trying to gather the internals individually so I can configure them as I wish. And I'm not specifically looking for M4 internals, I'm just looking for high-quality internals. I can modify it to take whatever internals there are, but I am only familiar with the M4. As I said I'm very new to this

[Red Dot]

This sounds very confusing, are you buying a bull-pup AEG to modify or you want to build one from the ground up without an existing rifle? If you are doing the former it wouldn't be hard, just seeing reviews on the models you are interested in should help steer you in the right direction however if I'm not mistaken a lot of bull-pup rifles have proprietary or limited availability to certain internal parts because of their design.

If you are going the latter route I wish you a lot of luck, I wouldn't even know where to begin without recommending you start with an existing design and develop the platform you want from there.

[SuperCriollo]

From what I gather, he wants to create a bullpup rifle from scratch, using M4 internals.

Anyway,


You will need a MOSFET in order to make your trigger mechanism work, since the trigger will move towards the front. Another thing that you should keep in mind is feeding, as creating a new mounting system for the gearbox and magazine can screw things up.

You don't really need an uberly long inner barrel for accuracy, as the bore quality is far more important.

[Devellis96]

Originally Posted by SuperCriollo

From what I gather, he wants to create a bullpup rifle from scratch, using M4 internals.

Anyway,


You will need a MOSFET in order to make your trigger mechanism work, since the trigger will move towards the front. Another thing that you should keep in mind is feeding, as creating a new mounting system for the gearbox and magazine can screw things up.

You don't really need an uberly long inner barrel for accuracy, as the bore quality is far more important.

The long barrel is for aesthetics. Which barrels would you suggest? What exactly is a mounting system? Couldn't I just move the gearbox to the rear and feed from the magazine as normal?

[ThunderCactus]

You could, but the trigger isn't going to stay behind the magazine if it's a bullpup or you're going to be holding it real awkward like.
You'll need to make a trigger housing and likely run it off a button switch which controls a MOSFET

As for barrels, you can't even efficiently run a 509mm barrel off a full cylinder, let alone a 600mm barrel.
The outer barrel may be aesthetic, but it doesn't mean you need to have an inner barrel to match. You can run a 10" barrel in a 20" outer barrel just fine. If you're not getting less than a 1mm grouping at 10" from your barrel, you've got some really serious accuracy problems to take care of lol
It's not going to increase your range or accuracy, either. 440mm is apparently the longest barrel you can run for best efficiency on a full cylinder.

[naminator]

Dude what?

An M4 uses a V2 mechbox. The motor goes into the grip.

I think you might be using the term "bullpup" incorrectly or are confused a bit. A "bullpup" rifle is one that has the firing mechanism behind the trigger. That means the Magazine is once again behind to trigger. I cannot imagine what your project goal is with this gun. If you are looking for a bullpup rifle that uses stanag magazines, get an L85/86 or a Tar21. What you are proposing would require massive amounts of machining and modification skills. The gear box is already behind the magazine on your G&G.



Honestly from what you are describing I don't think you would be able to accomplish. You can make your current M4 burst fire using a computerized board, but I would scrap the bullpup plan right now.

[ThunderCactus]

That being said, probably want to use a V6 mechbox where the motor is parallel to the barrel. Makes the overall mechanism shorter. But you'll still need to wire up a trigger

[Danke]

Step one. Get soda bottle.

[brock0]

Definitely a project where if you described your theme, or provided a sketch or reference photo, you'd get a lot more help.

[Devellis96]

Originally Posted by naminator

Dude what?

An M4 uses a V2 mechbox. The motor goes into the grip.

I think you might be using the term "bullpup" incorrectly or are confused a bit. A "bullpup" rifle is one that has the firing mechanism behind the trigger. That means the Magazine is once again behind to trigger. I cannot imagine what your project goal is with this gun. If you are looking for a bullpup rifle that uses stanag magazines, get an L85/86 or a Tar21. What you are proposing would require massive amounts of machining and modification skills. The gear box is already behind the magazine on your G&G.



Honestly from what you are describing I don't think you would be able to accomplish. You can make your current M4 burst fire using a computerized board, but I would scrap the bullpup plan right now.

I didn't ask for negativity. I'll post the picture when its done.

I know what a bullpup rifle is.. magazine and firing mechanism behind the trigger. That's what I want. I'm going to put the gearbox and motor in the stock and embed the magwell in the stock as well. I'm going to create my own Mofset unit --one that allows for safe, single, 3burst, auto

[L473ncy]

That's not how it works. That's not how any of it works.

I would really use a V6 gearbox in your case. But that's just me. Also I don't think you realize what goes into making a FET. Anyone can buy resistors, diodes, and a MOSFET to make a simple FET but if you want computer control you're going to have to add in a microcontroller and other stuff (probably the ATtiny AVR microcontroller) and get a programming cable and all that (and of course actually program the damn thing or at least flash someone elses already made firmware (such as DonP's TriggerMaster firmware or it's parent firmware the ExtremeFire which are open source)).

[Devellis96]

Originally Posted by L473ncy

That's not how it works. That's not how any of it works.

I would really use a V6 gearbox in your case. But that's just me. Also I don't think you realize what goes into making a FET. Anyone can buy resistors, diodes, and a MOSFET to make a simple FET but if you want computer control you're going to have to add in a microcontroller and other stuff (probably the ATtiny AVR microcontroller) and get a programming cable and all that (and of course actually program the damn thing or at least flash someone elses already made firmware (such as DonP's TriggerMaster firmware or it's parent firmware the ExtremeFire which are open source)).

I want safe, single, burst, auto. I was thinking I could use an low-medium voltage battery. Safe would physically disconnect the trigger from the motor and lock the trigger in place. Semi and auto would work as purchased. But how difficult would it be to hook up an additional connection that detours from the fire selector through a chip that simply cuts off the current after three cycles? 3 latches, a few transistors and a handful of diodes.

[ThunderCactus]

If you're on a mosfet, the only electrically safe system would be to use a mechanical relay to cut power between the motor and mosfet.
Regardless of whether or not the trigger is electrically disconnected, the mosfet can potentially still fire due to an electrical short (like water), or a current spike causing the mosfet to fuse closed.

Everyone wants burst, but you know who has burst? Nobody. Because burst fire is useless.
The problem isn't getting the gun to stop shooting after 3 shots, it's getting the gun to do it reliably and consistently. The comp determines the stop cycle from the cutoff lever cutting power to the trigger. Without the cutoff lever, there's no semi-auto.
So you need a sensor somewhere to relay back positional information on the sector gear. Either cut the part of the selector that disengages the trigger off and put a switch on it to cut rotations of the sector gear.
Or, like the triggermaster, setup semi-auto timing on startup with 3 semi auto shots and have the comp use a timing delay to produce burst fire.
Or, like the ptw, use an IR sensor to detect the position of the sector.

You can use an 11.1v lipo battery no problem. Just design your SW-comp to pulse the output so you can reduce motor speed in 10% increments.

[Devellis96]

Originally Posted by ThunderCactus

If you're on a mosfet, the only electrically safe system would be to use a mechanical relay to cut power between the motor and mosfet.
Regardless of whether or not the trigger is electrically disconnected, the mosfet can potentially still fire due to an electrical short (like water), or a current spike causing the mosfet to fuse closed.

Everyone wants burst, but you know who has burst? Nobody. Because burst fire is useless.
The problem isn't getting the gun to stop shooting after 3 shots, it's getting the gun to do it reliably and consistently. The comp determines the stop cycle from the cutoff lever cutting power to the trigger. Without the cutoff lever, there's no semi-auto.
So you need a sensor somewhere to relay back positional information on the sector gear. Either cut the part of the selector that disengages the trigger off and put a switch on it to cut rotations of the sector gear.
Or, like the triggermaster, setup semi-auto timing on startup with 3 semi auto shots and have the comp use a timing delay to produce burst fire.
Or, like the ptw, use an IR sensor to detect the position of the sector.

You can use an 11.1v lipo battery no problem. Just design your SW-comp to pulse the output so you can reduce motor speed in 10% increments.

The 3Burst is aesthetic, obviously I wouldn't use it in a real match. I just want it to be there.

I think the second solution would be the easiest and cheapest. So on burst, I'd pull the trigger once and the chip would need to pulse three times.

Can you clarify the first method you suggested? What exactly is the sector gear?

[ThunderCactus]

The sector gear is the one that pulls the piston back and releases it. It's also responsible for all the timing actions of the mechbox.
The downside to the timing method is it's never terribly precise. Especially if you're doing multiple bursts.
It's time based, so as the voltage lowers on the battery, the motor will slow, but the timing will not compensate for that.
It was a much more significant problem with NiMH batteries than LiPo though.