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Upgrading an EBB to Death

RIP EBB (Electric Blowback)

This bundle of parts in a body bag is the end result of all the upgrades and tampering I did to a Desert Eagle EBB. It’s all snapped housings and popped gears now.

At least the motor still works.



So you have an EBB pistol? You’ve doubtlessly noticed that it has very poor power, a laughable “blow back” effect, and a slow cycle time even with fresh batteries – it’s not too hard to pull the trigger faster than the gun can shoot.

Well, here’s how to turn that EBB into a fast-firing, crisp cycling, FULL-AUTO, high-velocity (for an EBB) machine pistol!

Oh, and of course in the end the gun died from all my upgrades, so ya takes your chances.

The theory is the same for all EBBs, but the one I used here is a Desert Eagle made in the USA by SoftAir. Doing all the upgrades I described resulted in the death of the gun, but you can perform at least some of the upgrades safely (or at least with minimal resulting abuse to the gun’s internals).

SUMMARY OF MODIFICATIONS

The total modifications are pretty straightforward – in fact, almost exactly (in concept) what you do to an AEG to upgrade it.

In the end I gave the pistol:

  • Full-auto capability
  • A select-fire trigger (pull to fire one shot in semi-auto, pull all the way back to fire in full auto)
  • Faster action (faster shooting action and “blowback” effect)
  • Increased RoF (rate of fire) in full-auto due to the above
  • MUCH higher muzzle velocity
  • A vastly shorter lifespan

The higher muzzle velocity was the single mod that most decidedly led to the EBB’s demise. You should actually be able to make the rest of the modifications with minimal problems. I’d do it if I had another EBB.
THE BATTERY UPGRADE

The battery upgrade consists of a modification to allow the gun to accept a 9V battery (which is really just a package of 6 cells, each a little smaller than an AAA cell) instead of the usual 4 AAA cells.

This can be seen on the left – it was done by cutting away the inside of the battery compartment until a 9V could fit where previously only 4 AAAs would. The Desert Eagle’s fat grips doubtlessly made this easier.

Feeding the motor more power by way of the 9V cell makes the motor run faster, which in turn makes the entire action of the gun work faster (increasing RoF and lowering cycle times).

Note that a 9V battery will not last as long as the 4 AAA cells.
FULL AUTO MOD

To give the gun full-auto capability, you can connect an additional switch to your gun so that the motor is connected to the battery terminals when you press the second switch. You can then use the second switch as a full-auto trigger (keeping the original semi-auto trigger) or you can put the two together to make an AUG-style select-fire trigger: pull for one shot in semi-auto, pull all the way back for full-auto.

Note that preserving semi-auto fire mode allows you to fire a couple shots in semi after using full-auto to make sure the spring is stored in a decompressed state.

First I’ll cover the connection of the full-auto switch. You will need:

  • Some wire
  • Soldering Gun and Solder
  • Momentary switch (preferably small and thin)

Take a look at the picture and you can see the switch I used hanging below the trigger guard.

Take a look at the connections between the motor and the battery compartment. One wire will connect a terminal of the battery compartment directly to a terminal of the motor. Locate the equivalent of this connection on your EBB – we will leave this connection alone.

It is the other battery and motor terminal that we are interested in.

This other battery terminal and motor terminal are connected to each other via a switch which is controlled by the trigger assembly. We will connect our full-auto switch between these two terminals, IN ADDITION TO the existing wires. In this way, pushing our full-auto switch will run the motor independant of the original trigger.

All that needs to be done is to connect the battery terminal to one end of our switch and connect the other end of the switch to the motor terminal. Done! You now have a semi-auto trigger (the original trigger which still works) and a full-auto trigger (the switch we just installed).

If you wish, you may connect the full-auto switch somewhere on the gun to use separately. But if you wish to make a select-fire trigger, you should mount the switch in the following way.

MAKING A SELECT-FIRE TRIGGER

To install your new full-auto switch so that you have a select-fire trigger, test your trigger to see how far back it needs to go to fire in semi, and locate the switch BEHIND the trigger behind that point – but not so far back that the trigger won’t push it.

You’ll need to trial-and-error it to find the best mounting point depending on your switch and your gun.

You may need to trim away the rear of the trigger and/or recess the switch somewhat.
INCREASING THE VELOCITY

Friendly note: this is what finally did my gun in. Attempt at your own risk.

Once the gun was open, the spring was easily accessed from the top of my gun. I could pop the spring out and do my worst – which consisted of adding a spacer behind the spring, thereby increasing power.

I cut a 7mm long segment of a suitably-sized brass tube and inserted it. A test fire worked fine, so the gun was reassembled and I fired wildly away for approximately 15 rounds before the gears ground and started spinning freely. Whoops. That was that. When I removed the battery little bits of black plastic (from one of the gears, I found) fell out.

Before the gun gave out, I could tell it was firing HARD just from the sound and feel. How hard? Well, I did not chrono it, but I did perform a non-scientific test that should speak volumes.

In stock form, the gun fired at a relatively low velocity (typical for an EBB) using .12g BBs. The built-in hop-up was quite good, and the gun was VERY accurate at about 20-25 feet.

I could fire at my bare hand and foot with only a very slight twinge of pain upon BB impact in stock form. After adding the spacer, though, things were a little different.

After re-assembling the gun and firing a couple rounds, I shot the tough part of my palm as a test.

YEEEOUCH!! Damn, that hurt! My palm had that “on fire” feeling that quickly gave way to a painful throb that didn’t subside for a good few minutes and left a nice red mark.

Didn’t have a chance to see what effect the increased velocity had on accuracy, either. As mentioned, the gun only lasted about 15 shots total.

UPDATES (Sep 4th 2002)

SPRING SPACER
From a little more digging, it looks like something else may have been more to blame for the stripping of gears besides just the spring’s increased tension.

In another gun I am looking at (a mini MP5) the spring is nearly fully compressed when the piston is cranked all the way back. *IF* the spring in the EBB was also almost fully compressed when the piston was all the way back, that means that a 7mm spacer – not being flexible – would have made further compression impossible before the piston was actually all the way back. That in turn means that the gears would have to be forced to slip in order for the gun to fire – chewing them up in the process. A few of those would be enough that last 1 or 2 teeth.

Don’t know if that happened on the EBB but it’s a distinct possibility. Watch for it if you are attempting your own spring upgrade.

FINAL WORDS

Well, there’s how to upgrade your EBB to death. I didn’t have a chance to try a smaller spacer, but I think that any added spacer will probably cause the most strain on the internals.

The rest of the mods, though (the 9V battery and the full-auto) worked just fine in my EBB for many rounds and would probably be safe to perform. Your mileage may vary.

Why it died: The problem was mainly stripped gear teeth due to the big spacer I originally put into the EBB’s spring. The 7mm spring spacer was too big – the spring was 100% compressed up against the (rigid) spacer BEFORE the gears had pushed the piston all the way back. That means that the gun needed to “hop” the last gear teeth to fire. It only took a few shots to wreck things.

I noticed that only the last tooth of the sector gear (the one that pulls back the piston) was stripped, along with the last tooth on the other teeth of the gear (the ones facing “into” the other gears).

I cut away the last gear tooth on the sector gear as well as the gear-tooth-track on the piston. This makes the piston release one gear tooth earlier than originally. This is good, since those teeth were messed up and slipping anyway.

To compensate for the shorter piston compression that results, I added a small spacer (4-5mm) which is a little shorter than the spacer that originally did the damage. I reassembled the gun and it works! Velocity even seems comparable to stock performance – maybe even a little harder.

Update: OVERDRIVEN FULLAUTO TEST

Not being able to leave anything the hell alone, I tested short bursts of fullauto on 12V. The thing absolutely pisses BBs, the slide whizzing back and forth in a blur. A nice ozone smell is generated.

Oh, and the piston doesn’t have a chance to actually return fully during the firing cycle – meaning that the BBs don’t go very far and are very low velocity.

And 12V on semi-auto is far too much – the gun fires and is halfway through firing the next shot by the time the slide comes back from the first. Kinda mucks up the whole operation of semi-auto.