Chronograph results

[ToddGeddes63]

I just got a Caldwell g2 chronograph. I have never used one and I could use some tips on how to understand the results. I'm shooting the Benjamin Cayden
22cal,I have the transfer port set half way. The PELLETS on test are CPHP 14.3 GR. 22cal. I set 2the caldwell about 5 feet in front of the rifle.
1st Do I have it too close? I didn't get any error messages and it seemed to read the shots good.
2nd I don't understand the results of the shot string, I could use your knowledge to help me understand the results. Thanks in advance for your help.

 

[ToddGeddes63]

I see that you can't click on the link to read all the information, the shot string was 48 shots from 3000psi fill, down to 2000 psi at 48 shots.

 

[davecole]

This is my take.
If the gun is new and regulated, there will be a break in period. I’ve had guns vary from 100 to 300 rounds. You’ll know when yours is because you will start to notice shots become duplicated if fps.
With the data you have here, if your zero was at 30 yards, the drop difference between the maximum and the minimum speed at 50 yards is less than 1/2”. At 100 yards, you’ll be 5” low. Depends on how far you’re going to shoot and how tight you need your shots to be.
What I do to determine exactly where my reg starts to fall off is to keep the gun tethered to the tank with the valve closed but not bled. Your supply tank gauge will be easier to read. (assuming you are filling from a tank) and watch for a steady decline in fps, say 3-5 fps with no recovery. I note that and that’s where I typically will start to refill the gun.
For general shooting purposes you want your extreme spread and standard deviation to be a bit closer together. A good number to try for is around 10 fps for SD (stand deviation). Your extreme spread will be proportional to that number. For disciplines like FT, my gun has an SD of 3fps but that’s over the top for hunting and backyard shooting.
My guess is, you’ll find your refill pressure to be around 30 shots.

 

[badger5th]

I'll try to help out.

#1 Being "too close" to the chrony is only an issue with powder burners. Unburned powder can result in errors on the high side since they are accelerated by the muzzle blast past the bullet once the bullet clears the barrel yeilding "false highs". It should be zero issue with air guns. It can possibly be an issue with CO2 guns from dry ice flakes yeilding high readings but should not be an issue beyond a couple of feet with CO2. Should be zero issue with air only.

#2 Is your rifle regulated? The extreme spread and standard deviation are similar to 40 shot data from my M-rod which is not regulated. The relatively low standard deviation indicates that the majority of your pellets were in a fairly narrow velocity range which is a good thing. Your average of 771 fps is just about equal the the halfway point in your extreme spread range which calculates to 777 fps. That indicates a very good parabola velocity curve with the peak right near the middle.

All in all IMO opinion your rifle is producing consistent performance.

 

[ToddGeddes63]

Thanks for the information, just so I understand correctly, I figured if the chrony wasn't giving error readings then it must be good, am I correct? or should I move it closer to the barrel? The Cayden is not regulated, at that fps using the CPHP 14.3 gr pellets, shooting out to fifty yards, my groups are dime sized. I wanted to see what the chronograph results show, compared to what I've determined from shooting, to be accurate, consistent, and group the best with the different pellet weights, and transfer port settings. My shooting results and the chrony results seem to show that I'm on the right track. Thanks for evaluating the results of the chrony, and helping me to understand what it all means. I have a lot to learn about a chronograph.

 

[badger5th]

Todd, One more thing I want to bring up. Your data is something like "777/0.00" The 0.00 is supposed to be the muzzle energy. If you input the pellet weight, the pellet ballistic coefficient (if you know it, there are online data tables of the BC values for every pellet made), and the exact distance of the chrony from the muzzle, It will give you a true muzzle velocity as well as true muzzle energy. Your pellet is slowing down a small amount in the few feet between the muzzle and the chrony. The App has the ability to correct for true muzzle velocity. Regards

 

[ToddGeddes63]

Thank you. I saw that there was more information I should have put in for a more accurate reading. I think that airgun magazine had some pellet bc information for each brand and weight of pellets. I will find the information and do another test. I appreciate you helping to understand this better.