Bulk fill vs 12g powerlets question/issue

[Geoff]

I have an umarex fusion and wanted to try bulk fill co2 on it.

I find that the first shot with the bulk fill is about the same as when I use the 12g powerlets.  After that there is a steep decline in FPS and I lose 100 FPS in the first 5 or 6 shots.

Is it normal that bulk fill from my 20oz Co2 bottle is not going to give me the same (i would have thought more shots since no carts are taking up space) FPS as 12g carts ?

Are the carts liquid filled and when I transfer from the 20oz bottle it is more gas than liquid so i am getting less volume by bulk filling ?

I like the idea of filling when it is low as opposed to swapping carts when they are dead, though I do not want to lose 100 FPS from it.

Thanks for any insight you can toss my way.

[Big Bore Bart]

  Bulk fill is weight based liquid filling.     All you have done so far it seems, is to gas fill.    Put the rifle on a scale then add ~25-30 grams of liquid CO2.     You may have to chill the gun to get the liquid in.

[Geoff]

thanks for the reply ...

does it matter if my 20oz tank is on its side, standing up or upside down for this ?

currently i have it tethered and planned to leave it like that for half an hour to see if it filled more.

inre weighting the rifle (too much trouble)  ... wont it fill to X no matter how long i leave it attached ?

[rsterne]

Your 20 oz. tank must be upside down so that you get liquid CO2 into the gun.... If you are only getting vapour, you will experience exactly what you are finding, very few shots and each one declining in velocity.... The amount of CO2 liquid that gets transferred into the gun will be depend on the temperature of the 20 oz tank and the gun, and ALL CO2 filling should be done by weight for safety.... Overfilling the gun can results in higher than safe pressures when the gun warms up.... This is particularly true if the gun was cold (colder than the 20 oz. tank) when you filled it....

Bob

[Geoff]

Thank you. 

Makes bulk filling kind of a pita to weigh the gun each time.

Edit to add :  after converting grams to ounces ..  25-30 grams .. i need a scale that shows pounds and ounces to know when i hit the ~1oz mark.   

[Ribbonstone]

One of the reasons I’m not a fan of bulk filling is that it’s hard to get in a full fill.  In the Fusion’s case, a full fill is not far off the 24gr. two 12gr. can give you (more like 28-30 grams).

20oz tank upside down and above the gun’s tank.
Gun COOLER than the tank.


Co2 has some great properties for airgun use, but some of those same things work against you for bulk filling.

Heat raises pressure.  As you start to fill the gun’s tube, are compressing gas into the tube, so the tubes temperature rises.  The 20oz tank is decompressing, so it’s temperature drops.  This is the OPPOSITE of what you’d want to get a good weight fill into the gun.

To get a half way decent fill, will need to arrange to have the gun cool and the co2 fill tank warm (not HOT).  In the winter, will stick the gun outside and the tank inside the warm house.   In summer, will reverse that and keep the gun inside the cool house and the co2 tank out on the back porch.

When out in the field, if I have my little cooler with some ice and water, will lay ice cubes on the gun’s air tube before trying to fill.

Now if you are just shooting from a bench and not moving around…why detach the 20oz tank at all?