TargetTalk

Just a post ... an FYI to all those that may end up shooting the 888 in the heat.

This week we had our NW District Contest here in New Mexico in Grants.
Our "Pellet Gun Superentendant" decided to shoot outdoors.
We had FULL, BRIGHT New Mexico desert sunshine and 98 degree temperatures ... leave the guns on the shooting mats and they get hotter.

We came prepared with 65 grams of CO2 in each 888 cylinder.

My Novices shot first, and after a few sighters in the prone, they moved on to their record shots. I watched in horror as their POIs began moving lower and lower until finally I could watch the pellets arc in flight. My youngest daughter was in tears as she kept moving her sights, up, up, and then topped out the sight ... all I could tell her was to shoot high.

I finally had her and my other novices declare a malfunction (halfway thru standing) and pulled their cylinders figuring I had massive leaks. They all weighed nearly full.

All I could think of was that the pressure in the cylinder got too high because of the heat, the hammer & spring could not vent any gas out of the cylinder.

I dumped 2/3 of the gas in each cylinder and replaced them and --- voile --- back to normal.

I'm so darn proud of those Novice kids, they had enough skill, and discipline to correct on the fly, keep shooting, and took second.

I dumped the cylinders for the Junior guns, and although they did not shoot their best (10 meters in 15 mph winds???), they took first.

So ... the lesson. IF YOU SHOOT IN THE HEAT & SUN WITH AN 888, max fill the cylinder with only 25 grams of CO2. We did not check, but I'm sure you can complete a 3x20.

I am curiouse as to how many of your 888s had this problem. My daughters 888 will pop the burst disc if it gets to hot and to much pressure. Also if it has just a little bit to much pressure it won't shoot at all until bleed some off. When she has to leave it on the firing line we have a reflective survival blanket to keep the heat off. County fair here shoots outside in August and usually hot.

I had 3 kids on the line and all three guns had the issue.

I am suprised that the burst disk did not blow, but there must be a zone where the pressure is too high for the gun to function, but too low to blow the disk.

I like the idea of the reflective blanket. The only issue I can see with it is that if you are using the new Clear Barrel Indicator (CBI) you might not be able to see the cord in the action and at the muzzle.

Maybe the solution is to use the reflective blanket, but cut it up and tape it to form a sleeve that covers the forearm where the cylinder is.

The only problem would have been that the sun heated the gun up in only about 5 minutes.

I'll use both ideas in the heat from now on ... half fill and the reflective blanket or sleeve.

Good idea.

i'd say the solution is to have the match director declare the pellet guy an idiot, and all shooters boycot the match until proper shade is supplied. it's downright cruel to keep kids and adults too in conditions like that. all you needed was a disc to blow in someones face while handling cylinders and take the sport through another rotc type of fiasco.

I could be very wrong on this topic.... but I can't help to wade in anyway.

Heat drops the vapor pressure of C02 - I think. Hot cylinder = low pressure.

I don't think that the heat increased the pressure in the cylinder - it dropped the pressure. Venting the cylinder would have chilled it - and returned it to normal function.

Perhaps I'm still confused.......

From chemists I get this explanation:
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CO2 is considered a volatile non-polar substance.

Increasing the temperature of a liquid increases it's vapor pressure not linearly, but LOGARITHMICALLY. Doubling absolute temperature increases pressure by a factor of ten times.

At about 40 degrees Fahrenheit, CO2 has a vapor pressure of 600 psi. At 72 degrees F, it's up to about 860. At about 80 degrees F, the CO2 vapor pressure rises to about 970 psi.

The critical zone is temperatures and resulting pressures above the "critical point," a unique combination of temperature and pressure for a given substance at and above which gas and liquid begin to behave the same, and normal fluid dynamics laws no longer hold. For CO2, this critical point is 88.88 degrees F, at about 1080 psi vapor pressure. It is unclear to science what state of matter the CO2 would be said to be in at and above this point - gas or liquid. At or above these temps, all bets are off as far as guessing the fluid behavior and/or the gas pressure of the CO2 inside the cylinder.

Bottom line - be very careful with heat and bottled CO2. If you leave it in a car, house, or closet with temps above 90 degrees or so, you are asking for big, big trouble. The only reason more people don't blow themselves off the face of the earth messing around with these compressed CO2 cylinders is because industry standard tanks are so tremendously over-engineered, to protect us from ourselves for both safety and liability reasons.

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I think I'm using 3500 psi burst disks. (That's what Daisy installs) I've only had one let go, and it was pretty dramatic ... scared the heck out of the shooter, gas venting to the left and right.

More reasons to cover the gun ....

Anonymous wrote:i'd say the solution is to have the match director declare the pellet guy an idiot, and all shooters boycot the match until proper shade is supplied. it's downright cruel to keep kids and adults too in conditions like that. all you needed was a disc to blow in someones face while handling cylinders and take the sport through another rotc type of fiasco.

Well, although I don't really like having the kids shoot in the sun, that's 4-H here in NM.

I should have (I had thought about it) had a practice out in the sun before we went, but I did not want to "stress" the kids out ... it takes a lot out of you to sit out in the sun, even at 6PM here.

I wonder if we could have brought those big ol' 12x12 shade rooms to the line....