Umerax magnum research baby desert eagle power modification

[aslanshow]

So as a new member I don't have picture posting privileges, I'll just have to be super descriptive.
The baby desert eagle is an inexpensive co2 powered repeating pistol with a 15 bb "magazine"  along the top of the barrel enclosure.
Stock it's rated for 420 fps. I recently had it apart and figured out a power mod.
It's held together by Phillips screws, a long one at the muzzle end (under spring pressure, careful) and a small one on the hammer, one for the picatinny (don't lose the anchor for this one)  and the other half dozen are the same size.
The action goes like this, the trigger pushes the barrel forward past the bb feed and against the spring encircling the barrel, when it breaks the barrel slams back loading the bb then pushing in the co2 valve, co2 released, bb flies, tin can dies.
The co2 valve has a nipple for the cartridge feeding a fairly big chamber, a nail shaped pin is held by the valve spring sealing the hole on exit side, the shaft feeds through the hole and protrudes outside as the pin. The shaft of the pin is hollow almost to the head where it connects to a hole through (perpendicular to) the shaft (I'll call this the exit port). Pushing the pin into the valve puts the exit port into the co2 chamber which flows through the exit port, down the pin through a collar into the barrel.
Some might try increasing the strength of the barrel spring thinking they could open the valve longer. Not so much, there is a collar, a hollow stepped cylinder that pushes the hollow valve stem on one side and gets pushed by the breech end of barrel on the other. This collar only allows the valve to be pushed in about 1/2 a mm. Checking the inside of the valve I found that only about 1/3 of the exit port was exposed with this little motion. So no matter how strong a barrel spring you had the collar prevents it from opening the valve further.
If you reduce the length of the collar on the valve side (the larger diameter side) you can increase the co2 output. The valve stem gets pushed further, exit port opened more and valve open longer. I figured taking off about 1 mm would fully expose the exit port on the inside of the valve.
I took it down about 0.6 mm and it seems extra punchy. Gonna run through co2 faster but I found this guy would still have tons of co2 after I was done shooting, usually one cartridge would last 3-4 sessions.
I need to make a chronograph so I can give real numbers.
One might also try enlarging the exit port and id of pin and collar
I hope that's clear enough, if not ask questions.
Thanks y'all

[Toddspeed]

Ive never had my Crosman PFM16 apart, but I think it works the same way as your Desert Eagle. I’ve often wondered why I’ve never read about these CO2 pistols being modded. I might have to take mine apart and look into enlarging the port that lets gas flow through the piercing pin to the valve. I can’t imagine there is much plenum there, so allowing more gas through the piercing pin might have a considerable effect on velocity.

Maybe we can start a modding trend, who can get the most FPS out of a semi-auto CO2 BB pistol.

[superchikn]

I like the part about "I need to make a chronograph"   

[Tucobenedicto]

So as a new member I don't have picture posting privileges, I'll just have to be super descriptive.
The baby desert eagle is an inexpensive co2 powered repeating pistol with a 15 bb "magazine"  along the top of the barrel enclosure.
Stock it's rated for 420 fps. I recently had it apart and figured out a power mod.
It's held together by Phillips screws, a long one at the muzzle end (under spring pressure, careful) and a small one on the hammer, one for the picatinny (don't lose the anchor for this one)  and the other half dozen are the same size.
The action goes like this, the trigger pushes the barrel forward past the bb feed and against the spring encircling the barrel, when it breaks the barrel slams back loading the bb then pushing in the co2 valve, co2 released, bb flies, tin can dies.
The co2 valve has a nipple for the cartridge feeding a fairly big chamber, a nail shaped pin is held by the valve spring sealing the hole on exit side, the shaft feeds through the hole and protrudes outside as the pin. The shaft of the pin is hollow almost to the head where it connects to a hole through (perpendicular to) the shaft (I'll call this the exit port). Pushing the pin into the valve puts the exit port into the co2 chamber which flows through the exit port, down the pin through a collar into the barrel.
Some might try increasing the strength of the barrel spring thinking they could open the valve longer. Not so much, there is a collar, a hollow stepped cylinder that pushes the hollow valve stem on one side and gets pushed by the breech end of barrel on the other. This collar only allows the valve to be pushed in about 1/2 a mm. Checking the inside of the valve I found that only about 1/3 of the exit port was exposed with this little motion. So no matter how strong a barrel spring you had the collar prevents it from opening the valve further.
If you reduce the length of the collar on the valve side (the larger diameter side) you can increase the co2 output. The valve stem gets pushed further, exit port opened more and valve open longer. I figured taking off about 1 mm would fully expose the exit port on the inside of the valve.
I took it down about 0.6 mm and it seems extra punchy. Gonna run through co2 faster but I found this guy would still have tons of co2 after I was done shooting, usually one cartridge would last 3-4 sessions.
I need to make a chronograph so I can give real numbers.
One might also try enlarging the exit port and id of pin and collar
I hope that's clear enough, if not ask questions.
Thanks y'all

This can help?

[aslanshow]

Yes, thanks for the parts diagram.
The part I modified is part 28 in the diagram, the larger diameter end.
I just chucked it in my drill press and poor man lathed it about 0.5mm . It was a little rough but only the id passes gas. I need better files.
Not a lot of people wanna develop mods for the cheap co2s (at least not like the 13xxs). I suppose there's only so much you can do. Each one is different too. I have 3 co2 pistols and each one has a different mechanism for doing the same thing.
On co2 passing, would a rough path not be better than smooth. Counter intuitive as most of the time we smooth air paths. But if co2 encounters friction it creates heat which assists in co2 expansion, dunno any thoughts?

As far as "make a chronograph" goes the theory is simple enough, fast clock 2 triggers and I'm sure I've got most of the parts in my shop already. I've checked out some diy chronys and I'm kinda surprised I haven't found an open design project on here for one... guess I need to make a new topic.

[Tucobenedicto]

Never tuned a co2 pistol this kind,but you still increased valve lift,the only two things left are ensure a better flow and increase percussion spring rate a bit.Increase internal valve volume can help,but i don't see how in this kind of small valves.

[Pelletjunkie]

I think you modding a co2 pistol is cool. But a chronograph only costs as much as your 3 co2 pistols so just buy one so you and the people that read your posts can have faith in your velocity numbers.

[superchikn]

Frank,

I'm thinking that the fact that he wants to whip one up seemingly like changing a CO2 cartridge, leads me to believe someones talents run deep.

Build away Asianshow!!!

[Timplusten]

Aslanshow,

I'm new to the airgun scene. (four years or so) Especially new to the internals.

Wondering if you could provide some guidance in regards to reassemble of the umarex baby desert eagle c02 postol. I performed the mod you speak of in the first post. Upon disassembly, I didn't get a chance to view the orientation of the trigger spring as it came apart while splitting the halfs. Well, the pin came out with the upper half and now I have no idea how this spring fits in. Love the gun, it has been flawless so far and I've owned/used it for just over 4 years. Even an internal picture of the gun assembled would work. Just need a birds eye view of the parts fitment.

Thanks in advance.