Plenum Size Does Matter !!

[SpiralGroove]

I know this has been discussed before, but kinda shocked that adding just a 20cc plenum to my .25 caliber RAW HM1000x gave me 1011 fps with 34 grain JSB's (77 fpe) using OEM spring.
The set-point has always been set at about 150 bar, but w/o the additional plenum ... same set-up maxed out at 930 fps.

The additional plenum had been on another lesser caliber gun, but felt it belonged on the higher powered gun.

Going to lower regulator set-point to about 140 bar with the idea of getting the gun to max out at around 940 fps. Trying to tune to about 910 fps for efficiency/low ES, knowing the gun can generally shoot 1 MOA at said velocity.

 

[Airgunmann]

My pre air force came out to about 120 bar at 905 ish with 34 jsb is what I had it tuned to before I sold it plenum size can make a big difference

 

[AmosBurton]

The whole in my wood stock is the reason I don't have a larger plenum, yet...
Where does one get one of those?

 

[SpiralGroove]

The whole in my wood stock is the reason I don't have a larger plenum, yet...
Where does one get one of those?

Mubhaur makes them out of SS, with the plenum exiting via a hole drilled through the stock. Please contact him on AGN.

My 20cc plenum was made from a threaded Co2 cartridge screwed/soldered into a piece of brass stock. The plenum is hidden inside of the gun stock which was hollowed out using a Dremal, to make space where the plenum sits. The brass portion is screwed into the receiver where the blanking plug goes.
The cartridge end faces the muzzle of the gun.

This is very DIY, but safe if done carefully; I received guidance from Bob Sterne on safety parameters.

Other members may feel this is too risky for their blood.

 

[Stubbers]

I've been running one of these for years on my maruader, albeit a larger 33 cc version...works a charm.

-Matt

 

[mubhaur]

Mubhaur makes them out of SS, with the plenum exiting via a hole drilled through the stock. Please contact him on AGN.

My 20cc plenum was made from a threaded Co2 cartridge screwed/soldered into a piece of brass stock. The plenum is hidden inside of the gun stock which was hollowed out using a Dremal, to make space where the plenum sits. The brass portion is screwed into the receiver where the blanking plug goes.
The cartridge end faces the muzzle of the gun.

This is very DIY, but safe if done carefully; I received guidance from Bob Sterne on safety parameters.

Other members may feel this is too risky for their blood.

View attachment 373771

I am also concerned on safety on your set up.

I hope you would have tested it at least double the bottle pressure that means at around 500 bars as the regulator can go bad any time and in that case you should have 100% safety factor at least.

Further since your setup takes 90 degree bend, being the tiny bottle attached at right angle, the air throw to the valve would take a sharp tun and resultantly the potential of power will decrease.

Further the tiny bottle mouth is so small that it would Further cause a bit of bottle neck for air flow.

My greatest concern is your safety, the other matters I discussed are just for sharing.

The more tunrs the air takes, the power thrust of air becomes decreased accordingly.

It's like turbo engines.

Regards,

Bhaur

 

[Stubbers]

I am also concerned on safety on your set up.

I hope you would have tested it at least double the bottle pressure that means at around 500 bars as the regulator can go bad any time and in that case you should have 100% safety factor at least.

Further since your setup takes 90 degree bend, being the tiny bottle attached at right angle, the air throw to the valve would take a sharp tun and resultantly the potential of power will decrease.

Further the tiny bottle mouth is so small that it would Further cause a bit of bottle neck for air flow.

My greatest concern is your safety, the other matters I discussed are just for sharing.

The more tunrs the air takes, the power thrust of air becomes decreased accordingly.

It's like turbo engines.

Regards,

Bhaur

Those co2 carts have been tested to fail around 9000 psi iirc so plenty safe.

 

[JaceSpace1369]

Those co2 carts have been tested to fail around 9000 psi iirc so plenty safe.

I'm sure the worry isn't so much the c02 cart, but the weld itself.

 

[TerryE1]

I'm sure the worry isn't so much the c02 cart, but the weld itself.

Agreed.

 

[thomasair]

I’m guessing the threads are doing the work, and the welds are just extra insurance. It doesn’t take much thread to safely hold a very high axial pressureload. Since the threaded portion is necked to a pretty small diameter it may only be needing to hold 300 lbs of axial force to be safe to 5000 psi. Doesn’t take much thread to hold 300lbs.

The numbers above are just approximations to illustrate the axial force…please don’t take them as exact figures.

Mike

 

[pnwairgunner]

It looks like a prototype or a proof of concept thing to me. I’m glad that it’s working for you and I hope it serves you well, but I would not want to use it myself. Looks scary to me.

 

[SpiralGroove]

Yes the Co2 cartridge is threaded into the brass stock, the solder seals any air leaks and gives additional strength to the joint.
Completely enclosed in stock so can't be bumped.

I've been using this for about 2 years now on my RAW.

Yes, all the right angle turns hinder air flow, but it's marginal. The Co2 bottle neck hole is the size of my TP.

Again, not for everyone - but the gun now has about 50cc's of plenum which very much helps on the shot in .25 caliber.

For most (non-tinkering) people wanting additional plenum space, mubhaur has the best functioning plenum.

 

[AmosBurton]

@SpiralGroove - Thanks for the info! I guess it's time to take apart my gun and see if the stock has room for something similar.
I really don't want a plenum sticking out the bottom of my wood stock if I can help it.
If it does have enough space, I'll be looking for that 90 degree fitting.

 

[SpiralGroove]

@SpiralGroove - Thanks for the info! I guess it's time to take apart my gun and see if the stock has room for something similar.
I really don't want a plenum sticking out the bottom of my wood stock if I can help it.
If it does have enough space, I'll be looking for that 90 degree fitting.

Yeah, if mubhaur's plenum could be hidden in the stock it would be very appealing to me. Plus, FX has shown the benefits of a 70+ plenum.
While my contraption looks like something cobbled together from a science project - it works well.

 

[Stubbers]

Yeah, if mubhaur's plenum could be hidden in the stock it would be very appealing to me. Plus, FX has shown the benefits of a 70+ plenum.
While my contraption looks like something cobbled together from a science project - it works well.

Lol I posted on the forums plenty of graphs proving plenum benefits long before FX took that train, in fact my picture above is 5~ years old mate..not to say I am taking credit but FX definitely does NOT deserve credit.

-Matt

 

[Stubbers]

Effect on plenum size... 25 cal marauder

 

[Deleted member 50932]

Mubhaur makes them out of SS, with the plenum exiting via a hole drilled through the stock. Please contact him on AGN.

My 20cc plenum was made from a threaded Co2 cartridge screwed/soldered into a piece of brass stock. The plenum is hidden inside of the gun stock which was hollowed out using a Dremal, to make space where the plenum sits. The brass portion is screwed into the receiver where the blanking plug goes.
The cartridge end faces the muzzle of the gun.

This is very DIY, but safe if done carefully; I received guidance from Bob Sterne on safety parameters.

Other members may feel this is too risky for their blood.

View attachment 373771

I’m not scared, I’ve done dumber sh*t on two wheels lol.
Show me how I can do this to my PROD!!

 

[Stubbers]

On mine, I drilled out my plenum/gauge block so that it breathes equal to my porting in the gun. I also opened up the 90 degree adapter to .234" as it was a bit under.

I gained about 50 fps / 8 FPE going from 20 cc to 53 cc on my marauder.

For the gent who claims there is much loss having the air turn 90 degrees, you know non-axial valves which what nearly all airguns use have the air take not one, but TWO 90 degree turns from valve to barrel? heh...

-Matt

 

[SpiralGroove]

Lol I posted on the forums plenty of graphs proving plenum benefits long before FX took that train, in fact my picture above is 5~ years old mate..not to say I am taking credit but FX definitely does NOT deserve credit.

-Matt

Yes Matt,
I know ... because I used your graph/results in deciding if my plenum would be worth the effort/risk .
The biggest problem I faced was cutting BPS threads in the brass stock on my lathe.

 

[SpiralGroove]

Hey Prop-ganda,
I would make something like Matt did above using existing pipe fittings.
The trick is to hide it in the stock ... if you wanted to.