Author Topic: bulk filling co2 airguns  (Read 146 times)

Offline Dvlnme

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bulk filling co2 airguns
« on: December 02, 2018, 10:54:19 AM »
Tired politics so time for something completly unrelated to politics,some time ago I made up some bulk
 fill co2 cylanders for the Gamo G1200 and co2 extreme rifles i use controlling pest birds in warehouses
 etc,I had some major issuses get effective seals in fill valves,due to I found out using the wrong
 material for the seals,Having no finally resolved the seal ussues,the fill valves are now working and sealing
 as should do.Chronoing both guns brought up some interesting things,now having 36 grams of liquid
 co2 in a rifle that nornally used 12 gram disposibles,completly changed how this rifle performs,40 full power
 shots was normal from 12 grams,was expecting to get approx 120 shots from 36 grams being three times
 the previous capacity,that turned out to right,but it completly change how rifle performed,right from first
 shot and for 120 shots velocity stayed within the usual 535/545fps it normaly gave for approx 35 shots
 and didnt drop off until all the liquid co2 had run out,pretty pleased with that,as normally on 12 gram
 disposibles velocity started to drop of bout 30 shots,dont understand exactly how pressures work with
 small co2 sources but assume it got to do with amount of liquid in cylander to some degree,
 What became obvious to me was the larger amount liquid in 36 gram cylander seemed keep pressures
 more constistent and didnt really change until all the liquid was gone,then velocitys dropped pretty much
 instantly,rather than slowly as with 12 gram over the last 10/12 shots etc.
 Wasnt chasing extra power in either rifle just better economy,but end result being the accuracy has got
 significantly better and so good in first place,interesting if nothing else and got nothing do with politics
 which is like kicking a dead horse ,that kicking isnt going to change the fact its dead eh!!
 Mintie you the co2 man thought this may interest you,as bulk filling seems have other advantages than
 economy that i wasnt aware of.
 cheers mike

Offline Mintie

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Re: bulk filling co2 airguns
« Reply #1 on: December 03, 2018, 11:03:49 AM »
CO2 is interesting stuff, you probably know this stuff but I will outline its properties in terms of airgun performance for other future sody enthusiasts.

 - The pressure of the gas CO2 changes quite a bit with the ambient temperature, nominally its around 850psi, As the temp drops so does the pressure.
 - So long as there is liquid CO2 in the vessel the gas CO2 will be at a constant pressure (depending on temp)
 - As each shot is taken and the pressure of the gas CO2 in the vessel drops the liquid evaporates to replace the gas to the same pressure, this evaporation causes the vessel to cool down rapidly
 - The amount of temp drop per shot is relative to the size of the vessel and how much gas you are removing from the vessel for each shot. For example if your valve is using enough gas to need .2 grams of liquid CO2 to evaporate to replace the gas used for each shot and the vessel is only 12 grams then that vessel will cool down much more with each shot than the same valve working with a 36 gram vessel as the percentage of gas taken to vessel size is 3 times as much.
 - CO2 cool down is what kills accuracy and performance in rapid fire applications that use 12 gram cartridges, each rapid shot drops the temp further and further which drops the pressure of the gas CO2. I have recorded more than 200fps (from 380fps down to 160fps) difference between shot 1 and shot 8 of a CO2 pistol fired quickly. 2 ways around this are much slower shooting which allows the vessel temp to come back up to room temp (or you can help it along with hand warmers etc) or a larger vessel which will handle the drop in pressure better because of the bigger ratio of gas taken per shot to liquid present to evaporate and replace it.
 - High powered applications can also cause temp to drop dramatically with each shot too, A maxed out 2250 will only get 10 shots per 12 gram cartridge so the amount of evaporation required to replace the gas from each shot is huge.
 - Power can be linked to barrel length and also pellet weight, CO2 expands at a slower rate than HPA so the longer barrels give it more of a chance to expand to its best potential, heavier pellets also give it a chance to expand more with a bit more time before they leave the muzzle so tend to produce more FPE

When the liquid CO2 has all been evaporated the pressure of the gas drops off very quickly with each shot, and this is where some CO2 gun designs are much more efficient than others - Take the Crosman 2250 as an example where the cartridge is pierced directly into the valve VS the QB where 2 cartridges are both pierced and fill the whole tube with pressure. The QB will end up depleting the liquid CO2 much faster as it has had to evaporate to fill the whole tube with gas before any shots are taken, it will still shoot fine while there is still some liquid CO2 left but once the liquid is gone the tube full of gas will drop power fast with each shot.

CO2 is a very good power plant for airguns as it essentially self regulates to a constant pressure so long as there is enough time given between shots for the temp to stabilize. It can be tuned in most setups to achieve 12fpe and more if you really want to push it. Its just a shame it cant really produce the same sort of power as HPA.
Lots of airguns

Offline Dvlnme

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Re: bulk filling co2 airguns
« Reply #2 on: December 06, 2018, 09:17:16 AM »
Like Mintie I have a soft spot for co2,I dont expect nor want the same performance from co2 as I get from
 hpa,my co2 guns are used mainly for shooting pest birds inside buildings at relaltivly short distances,birds
 are easy to kill with a well placed 177 cal pellet at quite low velocitys and fpe levels,I allso dont want a
 gun thats powerfull enought th drive pellets thru roofs/walls etc or damage builings in any way,so tend to
 flat nosed target pellets weighing 7,5 grains at approx 540 /750 fps at max,co2 does this very nicely.
 I origionally bulk filled my two gamo rifles foe ecomomy,not so I could modify them to increase power as
 I am very happy with one rifle at 5fpe the other at 8.5fpe on co2.
 Having these rifles on bulk co2 makes them like pcps cheap to run,able to be recharged whenever needed,
 as I have a large supply of bulk co2 in form of co2 fire extingishers I get free from my local rubbish dump
 so I will very likely ever run out of co2,As Mintie has said co2 is self regulating so can be very consistant
  and in accurate rifles just as accurate as a pcp costing many times more,I couldnt justify buying a pcp
  rifle for what I use the co2 rifles for and proberly coundnt find fast cycling pump action pcp repeating
 rifles any way that could match my co2 rifles.
 I am very much a pcp guy,but bulk filled accurate fast cycling co2 rifles work very well for me and what I
 use them for.and bonus is they are awesume fun plinking rifles as well.
 cheers mike