Co2 Powerlet performance Vs temperature

[Damo666]

I've just been to my local shooting range for a couple of hours & there's no heating on in there, only marginally warmer than outdoors as it's based in a large disused mill.

Over here in the UK, it's currently 4oC (39F) outside, and I'm guessing it's not much warmer in the range at circa 7oC (45F). It may even be cooler in there. 

I chrono'd my 2250XL (Co2) at the range, but was disappointed to see the results come back as 7.25 ft/ib - 477 FPS on a SKAN chronograph which I'm led to believe are accurate.

Normally, at home, at around 19C (66F) I've chrono'd my 2250XL, and the results come back as around 9ft/ib, - 520 > 535FPS on an LMBR R2A chrony through a series of shots. This fits in with the spec' & other people's findings.

Can a 15c reduction in temperature over about 1.5 hours really see a drop of nearly 2ft/ib or is my gun developing a problem?

[Kerndtc]

Totally. I'm actually surprised it didn't drop more power.

Here is a snap from a C02 Pressure temperature chart. (In °F)

Looks like almost a 200psi difference.

Cam

[Damo666]

Totally. I'm actually surprised it didn't drop more power.

Here is a snap from a C02 Pressure temperature chart. (In °F)

Looks like almost a 200psi difference.

Cam

Hi Cam,

Thank you for the reply.

Is there any way of correlating reduction of FPS or Ft/ib in relation to what you've shown?

IE - How many FPS reduction is likely with the 200psi drop?

[Frank in Fairfield]

I do not shoot CO2 in the Winter months..

[Tom Tucker]

Pressure and Muzzle Energy are directly correlated.  The only catch to that is that the valve will be easier to knock open when pressure is low, so lift and dwell will increase as pressure drops, partially mitigating the decrease.  So 1/2 the pressure should be a bit more than 1/2 the energy (and therefore also a bit more than .707 times the velocity).  There is also a point above normal room temperature where the pressure is high enough to cause partial or even total valve lock in some guns.  Whether or not that ever becomes a practical consideration depends on the gun and the tune.

[Insanity]

Bob has a very nice chart with Co2 range vs licquid to gas along with what stage it is in for the ambient temperature. You could try heating it up with say a hand warmer maybe even a thumb throttle warmer like that was discussed in another thread.

[Toddspeed]

Below is helpful chart, notice that at 80 degrees F, there is a nice flat line showing consistent pressure until it starts to drop off as you start to run out. Then as already pointed out, as temp goes down, the psi drop is pretty drastic.

[WyoMan]

Hi Damian, your 2250 looks to be running normal in the stock tune setup... i.e. over-sprung hammer. However, you can tune it to deliver a consistent fpe over a 30 deg temp range. If you think about it, the operating psi is only dropping by about 33% or less with the temperature change. PCP tuning is done all day long thru that pressure range. CO2 tuning for temperature and the corresponding pressure change is similar. The main difference is due to the cooling effect of CO2... you have to adjust the hammer strike a little further down the curve... that's about it in a nutshell.

If this is something you might want to do there's lots of help here. It will mean changing hammer springs and/or getting a power adjuster. And you will have less than maximum power at the higher temperatures... but you'll get better shot count!

Wyo

[Damo666]

Great replies, so many thanks.

On the said day, I'd just bought a new Hawke Vantage scope & zeroed it in at 20 yards - but after about an hour, I noticed my POI had dropped about 1 inch.

POI was fine at 10 > 15 yards.

I think I'll invest in a cheap springer & pack the 2250XL away until April when the weather warms up here.