LP1 Help! CO2 cylinder change causing site adjustment???????

[darticus]

Ayone ever see this. I have a cylinder in the gun and its shooting fine. The cylinder runs low and another full cylinder installed. I have to change rear site 15 clicks towards T as I'm getting low hits. Now it fine again, but 15 clicks???? What can cause this? Is it normal to adjust the site after a cylinder change. Any suggestions???

[GaryN]

If you don't let the first cylinder go down so low that the POI is changing, it should not. I can change the cylinder on my CPM-1 any time w/o affecting POI.

Wait, you said with the NEW cylinder it is shooting LOW ???

Mark the cylinders.
Shoot with cylinder A, then B
Then change the order, B then A

Is the low point of impact following the cylinder or is the 2nd cylinder always shooting low?

If it is following the cylinder, you might have a problem with that cylinder that is limiting the flow of gas.

[darticus]

Will have to fill both and label them than shoot from both and see. Thanks

[darticus]

Is it possible that an empty cylinder weighing less and the heavier new cylinder cause your hand to be weighted and shoot lower. 2 hours later I was able to go back 15 clicks and it was fine. I was not used to the light weight. Ron

[RobStubbs]

Is it possible that an empty cylinder weighing less and the heavier new cylinder cause your hand to be weighted and shoot lower. 2 hours later I was able to go back 15 clicks and it was fine. I was not used to the light weight. Ron

I'd love to know how much compressed air weighs, but no 15 clicks is masses. I can only think it's a pressure problem somewhere that's causing it. Try chrono'ing the gun with both cylinders, especially if it happens again.

Rob.

[Richard H]

Is it possible that an empty cylinder weighing less and the heavier new cylinder cause your hand to be weighted and shoot lower. 2 hours later I was able to go back 15 clicks and it was fine. I was not used to the light weight. Ron

I'd love to know how much compressed air weighs, but no 15 clicks is masses. I can only think it's a pressure problem somewhere that's causing it. Try chrono'ing the gun with both cylinders, especially if it happens again.

Rob.

Compressed Air weight is very very small, but he is using CO2 which is does have a measurable weight (thats how you know they are filled).

Darticus
The weight difference would be so small I'd doubt that it should effect you POI that much. If you can like Rob says try checking with a crony to see what exactly is going on.

[jrmcdaniel]

On some guns, the cylinder can contact the gun rather than be touching only at the pressure connection. This can cause POI changes both with different cylinders and with changes in pressure (not a problem with CO2 but with PCP guns). Be sure that the cylinder is not touching anything except the pressure connection. This type of problem has been seen in field target modifications to standard 10M rifles.

[Anders Turebrand]

Most likely you have overfilled the cylinder slightly, the CO2 relies on the gas above the liquid for even pressure, if there isn´t enough room for enough gas to develop you will have low muzzle velocity, I remember how CO2 shooters used to weigh their cylinders after filling to avoid this.

/Anders

[darticus]

Still checking this pressure problem. All 3 of my cartridges do the same. Slow velocity when just changed. If I let it sit awhile it seems to be ok( next day). Still checking

[darticus]

Shot the LP1 after 1 hour sitting and it seemed to shoot fine. Back to normal. Any thoughts? Maybe Gun freeze???? Empty warmer cartridge to new filled cartridge????????????????????????

[Steve Swartz]

Could be a lot of things . . . following the "hoofbeats = horses principle however it is probably a temperature stabilization problem; frequently encountered when using a recently filled tank (made worse with any overfilling, even a slight amount).*

CO2 works great but there are several pretty strict rules (set by mother nature, not the ISSF!) that govern it's use.

Steve Swartz

The gas pressure above the liquid is constant, but pV=nRT still applies. Pressure varies widely with temperature, and if the vbolume above the liquid is too small. Too cold and/or not enough ullage space = very low pressure. Problem will solve itself over time (warms up) and/or shooting some shots (to remove excess liquid)

[Ed Hall]

I'm also thinking on the side of slight overfill. If you are weighing them, I might even suggest checking the scale accuracy. Try filling them .5 oz lighter. If you're chilling them first, see what happens if you fill at room temperature. Either of these tests will supply sufficient CO2 for many shots, but could verify if your current method/scale is allowing an overfill.

Take Care,
Ed Hall
U.S. Air Force Competitive Shooting Teams
Bulseye (and International) CompetitionThings

[darticus]

When I fill at room temp it doesn't seem to fill. If I freeze after freezing it fills quickly.Will try to fill again at room temp and try to under fill. Thanks Ron

[David Levene]

Just a quick thought as I can't remember you mentioning it (apologies if you have), are you weighing the cylinders after filling to make sure you have put in the correct amount of CO2.

[darticus]

I do weigh with a postal scale.I try to be within one gram of cartridge markings. Maybe its a freeze up for a shot time????

[darticus]

Shot great today, full pressure, right on. It might have to do with a temporary freeze up due to condensation, over fill of tank, expansion of a full tank in 10 degree higher heat. The sound of the shot when it happens tells you its only maybe 400 ft/ sec instead of 525ft/sec. I think I'll switch tanks the night before than shoot the next day. Is this typical of a CO2 gun? FORGETABOUTIT!

[Cricman]

Hey darticus,

Try this: When you refill, set the cylinder valve-end up for a minute and let the denser CO2 settle away from the valve end. When you replace the cylinder, keep the muzzle down, so none of the dense CO2 makes its way into the staging chamber on the pistol. Again keep the muzzle down for a minute. Then (and don't do this in a match), crack off 5-10 shots without a pellet. listen for the change in the muzzle report. This should get you to a kind of CO2 equilibium. I still shoot a CO2 FWB, but my C25 solves the dense CO2 problem by re-orienting the axis of the cylinder and valve.

Good luck,

cricman

[jipe]

If I remember well, filling procedure for CO2 is:
- put the cylinder in the fridge
- fill it
- check the weight since pressure is constant with CO2 cylinder as long as there is some liquid CO2 and enough empty space in the cylinder, pressure is no indication of cylinder fill
- wait it come back to room temperature

On top of that, the problem of having liquid CO2 in the valve of the cylinder and/or pistol is a known issue. With horizontal cylinders this may easily happen when the cylinder is very slightly overfilled, the pistol put in a bad position... Feinwerkbau made a version of their pistol with a vertical CO2 bottle instead of an horizontal cylinder to reduce/avoid that problem.

What you could do is to slightly underfill your cylinders, i.e. put slightly less CO2 weight in it. You could also totally empty your cylinders and check their empty weight to see if it is really the one marked on the cylinder.

The procedure proposed by Cricman is also very good to purge the cylinder and pistol valves of any liquid CO2.

[darticus]

Thanks for the tips. The last time I filled I let the cylinder sit over night than put it in the gun. It seemed find. I think your onto something here. Thanks Ron