Does heat affect muzzel velocity on a pcp?

[masmiffy 82]

After my recent encounter with our local plod and the armed response unit when pigeon shooting with the 12G I decided to check out the fps on my Titan .22 pcp

Did it yesterday afternoon in the garden, it was bloody hot!

Set up the chrony and was getting a reading of around 570 ft/sec which with 16.4 grain air arms fields equates to about 11.8 ftlb. So was reasonably happy.

I did on last check after finising my beer and clocked 595 ft/sec = 12.9 ftlb WTF?

 

I am gonna do a re-check when the ambient temp has dropped but it was a bit disturbing!

What was legal suddenly wasnt!

Any thoughts lads?

[venomviper 129]

hi ya buddy

yeah the heat can affect the flbs so you have to try to be careful on how the gun is set and what pellets its set to i dont know all the tec words for it and why it does but i try to set mine in the colder days at 11.73 and when getting hotter drop her to 11.53 that way i cover myself and stay inside the law but if the gun is left in the heat it will push her up a bit and 11.8 is high on a hot day but it will send her over once the sun is really out but as you said you have a crono with you and check the gun at stages which is the best way sorry if this dont help you but someone will give you all the tec stuff you need soon enough buddy

 

shay

Edited May 24, 2010 by venomviper

[chameleon 26]

Heat should'nt have any effect on your guns loaded pressure, your regulator should only allow it to except a legal amount of air, normally guns effected by heat are CO2's, but if you want to stay with in the law, it may be worth getting your gun checked

[zini 1,939]

Hi Mas buddy,

 

I have just read and noted that you are calibrating your rifle using Air Arms Field pellets but saying that they are 16.4 grain.

 

Unless you have different AA Fields pellets that are heavier than the normal AA Fields your data is wrong that you are producing pal.

 

AA Fields and FX pellets are actually 15.89 grains and so lighter than you worked out your data on. This is the data you need to use to get a really accurate calibraition.

 

This said your rifle shooting at 570 fps is actually 11.47 FP (11.5) which is pretty dam perfect so i would be really happy with that mate.

 

The reading at 595 fps is still over the legal limit as it is actually at 12.5 FP.

 

Si

[stevieskin 4]

Heat does affect muzzle velocity to a degree. Most PCP will show higher velocity when ambient temp is higher.

Conversely many will show a drop in power when used in the depths of winter.

Its not all to do with air temp either, its depends how the lubricants used in the gun react to temp changes.

There is a vid on from Cubbleycat on you tube about this. Shows very convincingly how just removing the factory grease and using a light oil significantly cut the power drop when used in winter conditions.

 

One other thing, if you are using a Combro, they are known to often give erroneous readings in bright and changing light conditions, something to do with them using infra red sensors. Best used in subdued constant lighting. My Crombo is most accurate, when compared with a Skan chrono, when I use it indoors in darkish surroundings.

[masmiffy 82]

Hi Mas buddy,

 

I have just read and noted that you are calibrating your rifle using Air Arms Field pellets but saying that they are 16.4 grain.

 

Unless you have different AA Fields pellets that are heavier than the normal AA Fields your data is wrong that you are producing pal.

 

AA Fields and FX pellets are actually 15.89 grains and so lighter than you worked out your data on. This is the data you need to use to get a really accurate calibraition.

 

This said your rifle shooting at 570 fps is actually 11.47 FP (11.5) which is pretty dam perfect so i would be really happy with that mate.

 

The reading at 595 fps is still over the legal limit as it is actually at 12.5 FP.

 

Thanks for the info mate I will check the actual pellet weight on my micro balance at work.

I was using the 'Extorian' pellet weight chart and calculator cos its on my home PC!

The 595 reading was taken after I had reassembled the gun after checking it was 'legal' and I suppose was taken about 20 mins after the last 570 reading.

 

Si

[masmiffy 82]

Hi Mas buddy,

 

I have just read and noted that you are calibrating your rifle using Air Arms Field pellets but saying that they are 16.4 grain.

 

Unless you have different AA Fields pellets that are heavier than the normal AA Fields your data is wrong that you are producing pal.

 

AA Fields and FX pellets are actually 15.89 grains and so lighter than you worked out your data on. This is the data you need to use to get a really accurate calibraition.

 

This said your rifle shooting at 570 fps is actually 11.47 FP (11.5) which is pretty dam perfect so i would be really happy with that mate.

 

The reading at 595 fps is still over the legal limit as it is actually at 12.5 FP.

 

Thanks for the info mate I will check the actual pellet weight on my micro balance at work.

I was using the 'Extorian' pellet weight chart and calculator cos its on my home PC!

The 595 reading was taken after I had reassembled the gun after checking it was 'legal' and I suppose was taken about 20 mins after the last 570 reading.

 

Si

 

 

Thanks for the info mate I will check the actual pellet weight on my micro balance at work.

I was using the 'Extorian' pellet weight chart and calculator cos its on my home PC!

The 595 reading was taken after I had reassembled the gun after checking it was 'legal' and I suppose was taken about 20 mins after the last 570 reading.

[zini 1,939]

No problems Mas buddy

 

Chronographs work best according to my instruction book that came with my F1 chrono on cloudy days mate.

 

On cloudy days you don’t need to use the diffusers that come with it.

 

On bright cloudless days then a white diffuser needs to be used or your readings will be slightly inaccurate mate.

 

Using a chrono inside under florescent lights is also very bad mate and will cause your readings to go wild.

 

Just so you don’t worry buddy sometimes when I am chronoing my rifle I will get 8 or 9 readings at around between 565 to 575 fps and then the odd one at 585.

 

When I get the odd one that doesn’t look right with the rest of the readings i discard it mate and only add the others up and then divide by however many i am counting before working out my power level in FP.

 

Si

[masmiffy 82]

No problems Mas buddy

 

Chronographs work best according to my instruction book that came with my F1 chrono on cloudy days mate.

 

On cloudy days you don’t need to use the diffusers that come with it.

 

On bright cloudless days then a white diffuser needs to be used or your readings will be slightly inaccurate mate.

 

Using a chrono inside under florescent lights is also very bad mate and will cause your readings to go wild.

 

Just so you don’t worry buddy sometimes when I am chronoing my rifle I will get 8 or 9 readings at around between 565 to 575 fps and then the odd one at 585.

 

When I get the odd one that doesn’t look right with the rest of the readings i discard it mate and only add the others up and then divide by however many i am counting before working out my power level in FP.

 

Si

 

 

 

Did a quick weigh up of the pellets today at work.

Over 10 pellets the weight I got was an average of 1.0236g with equals 15.7965 grains.

So I guess 15.8 is the weight to use for air arms field.

This being the case then 575 fps = 11.6 ft/lb

584 fps = 11.97 ft/lb

[zini 1,939]

Sorted then buddy

 

Si

[masmiffy 82]

Sorted then buddy

 

Si

 

 

Yep it seems so mate thanks for the help.

Now set at 11.8 ft lb [give or take]