Chrono - Am I doing this right?

[thornstein]

Hello all. I'm trying to chronograph my FX Indy Bullpup for the purpose of using Chairgun Pro as effectively as possible. I set up the end of the Indy barrel about 4 inches from the beginning of the Chrono "gate". I'm shooting the 18.13 gr. JSB Jumbo Heavy Diabolo. In the table below you'll see the starting PSI I pumped the gun to. It is unregulated and I'm not even sure if I can regulate when using the pump feature.

I then took 4 shots, charted them, and pumped the gun back to the next starting PSI. I totaled the 4 shots, averaged them, and then looked at the deviation from the fastest shot and the slowest shot (Hi/Lo on the chart).



From what I've learned on this forum, my guess is that a 4 shot string from a starting point of 180 PSI is my best pressure to start at and get the most consistent shots. Am I right? Am I doing this right?

Thank you for your advice.

 

[TonyT]

Your data parallels my experience with an FX400. My gun shows the most consistent velocity spread between 180 and 150 BAR.

 

[Zephyr]

Interesting. I have been told (and done) a shot string by pressurising the gun to its max working pressure and recorded each and every shot, noting pressure. If the gun is unregulated you can expect the fps to increase before dropping off. This is the curve people talk about. You then decide you want all your shots within 3, 10, 20 fps (your choice), which identifies the 'sweet spot' you will have heard mentioned. You can then choose the average or median fps value of this sweet spot for ballistics calculations. It also means if your sweet shot is between, say, shot 30 and 70, you can correlate the fill pressure to the 30th shot and only fill to that pressure.

Any one else?

A good YouTube channel is 'Airgun Regulators'.

 

[John "spysir" Blount]

 You've got it.
In Field Target ( 10 to 55 yards) an extreme spread of less than 20fps is required. Naturally a lower spread would be nice. If you plan on shooting 100 ( or more yards) the lower the spread the better!
"I" would start at your 180bar area and try firing 1, 2, 3, ? and figuring exactly when and how many pumps to keep the ES low.

John

 

[Sprocket]

I don't have a chronograph yet, so take this with a grain of salt. It appears to me that you only have half the info to find the "sweet spot". Shouldn't you do that test at a certain yardage to target to find out what speed a particular pellet flies at the best?
If you fired at a piece of graph paper with 1/4" grids mounted perfectly level on the backstop and recorded each shot in relation to POA you would then know what the correct fps is for your gun and pellet.
Maybe one or the other end of the curve is more accurate than using the center of the curve. Just a thought. 

 

[thornstein]

All great feedback, thank you. Keep it coming though. The more opinions the better. Thanks again.