Am I using the chrony wrong?

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josh3rd

josh3rd

Member
Apr 2, 2015
954
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Newark, Delaware, United States
Hey members I have a question. I chronographed my Pro Sport today with its favorite pellet, the 8.4 grain Air Arms Diabolo. They were shooting at an average of 763 feet per second. Two years ago I had sent her to a valued and knowledgeable member who made a good rifle into a great rifle. When he returned her she was shooting at 785fps. I wanted it to be a 12fpe shooter. His knowledge and skills when it comes to Air Arms springers had led me to believe that it may be the way I had set up my chrony and/or was shooting over it. 

So I am wondering could it be that my spring, which is a QX4600 with fitted guides made by Motorhead, is already getting tired? Or could it be the way I was shooting across the chrony? Or could it be just from the way I had the chronograph setup? Meaning did I have the chrony at an angle or was the rifle not level while shooting over the chrony? All I did was level it by eye. 

I am also wondering since the sun was setting and I did not have the diffusers over the sensors. I do not have an indoor lighting system so I am assuming maybe that could be the case. Nonetheless your input is greatly appreciated and valued. I hope to hear from you soon. Thank you

cross posted
 
Well,, I ain't no expert when it comes to air-arms. But I've always had to fix (whatever) at the moment. lol,Lawnmowers, window blinds,plumbing issues, wiring, bikes.industrial equipment,on and on. thems my credentials.So I advise that you repeat your test in the middle of a sunny day. Take note to look at the piston, pellet seal cup.Looks like a little hardened beeswax cup set in the piston that is shaped to conform to the breach,where you load the pellet into the barrel.( for under-levers ). Replace if damaged. The temperature effects the springs ability to release it,s energy and the spring lubricant is certainly a factor in the rifles performance. In cold weather the grease will act thicker which slows the spring and the piston down. Air temperature even effects pcp,s in multiple ways. So you may chose to test on a warmer day. That would be my 1st query. After that I would want to look at the piston seal,(requires disassembly), to see if it is damaged,is it dry?, have nicks,not uniform,looks damaged?. At the same time you'll be able to inspect the spring for any breakage. Good luck to you
 
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It is not that big difference between the two numbers, and you have had it for 2 years since the tuning, could be the temperature ,weather and the sun in the wrong place, and the gun settle down after some time with the speed going up and sometimes down, shoot some 20 shots over the crony and write down that string to see if there is a big sd, wait a couple days or until weather change and do the same thing again.
 
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My chrono is iffy in direct sunlight. On an overcast or hazy day it runs perfectly. I've also had good luck with the chrony itself in the shade with a clear sky above. 

If your gun lost only 22 fps in 2 years after a tune, I wouldn't be surprised. It may have just settled into that velocity. As long as it's consistent at that slightly lower speed, you should be fine.


 
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well i just got done chronying my prosport inside with the diffusers on and used 2 LED flashlights, 1 on top of each diffuser. I did this in the dining room with the ceiling fan light off if that matters. It came up with the same average of 763fps. H-768; L-758; Avg 763; ES 10; SD 3. Pretty consistent over a 10 shot string. Will take it outside later and do it again. Still accurate though. That pro chrony is pretty good in my book.

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