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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-18 20:28:57  

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


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Dieker
(@jeff-c)
Joined: 2 years ago
Posts: 28
2020-02-18 22:52:51  

Josh I really can't help you but I have a similar situation with a Bam 40 . that is a Chinese copy of a TX200 and I believe the same power plant as the pro sport. Now that gun is Chinese but a well known tuner put a 20 cal Lothar walther barrel on it and it is very sweet and accurate but low on power. I put a Vortek PG2 kit in it and the power is still very low. I have a real TX200 in 177 to compare. That real gun shot the 7.9s so hard I had to run 8.4 pells to keep it around 900 fps. Anyways my 20 cal gun sounds real good and has good seaLS and is accurate so the only thing I can think of is a tight barrel. I believe all TX guns use the LW barrels. If you had not got that gun worked on I would have guessed a broke spring. A spring can break and kinda screw together and be weak with showing no signs of grinding. I personally would hate to put a stiff spring in such a gun. As far as the chrony goes the only way to test it is to shoot under some one elses chrony and compare. Also if you have other guns and if they shoot about right then its probably not the chrony. My chrony gives me the highest number on cloudy days. If its in direct overhead sunlight I always put some kinda shade over it. It just don't work right under direct sunlight and I can't see how those little shade strips they come with help at all and might put shade on one end and not the other. My shade screens got brittle and broke anyways like all plastic stuff. There is also the thought that the piston end cap leaks or the comp tube aint true but I very much doubt that and if it did leak it would not sound or shoot right IMO. I just remembered I have a bam 40 in 177 and it shoots way over 900 fps. Not super accurate though without real good Crosman premiers that I don't have. the point being the oem spring in those guns put out tons of power. way over 12 ft lbs so a stiff spring is not the answer..  Its a mystery. You should put new breach seals in it since that is just 2 orings stacked and not expensive. Some TX guns eat those orings a lot. I been lucky with my TX. Sorry I can only commiserate and not really help.Jeff C


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pluric
(@pluric)
Joined: 2 years ago
Posts: 679
2020-02-18 23:31:00  

If the chrony is reading a speed I doubt you are shooting across it wrong. It would read "Err". I've tested three chronys together in a row and had reading differences of up to 20 fps. 

I would judge it by what speed consistency you are getting with the chrony you are using. If the spread isn't bad and the accuracy is good don't lose sleep over it.


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-19 00:36:50  

Jeff, 1st of all I always wanted an B40. A "poor man's TX", so it fits me to a "T", lol.  And you mentioned the sun being out and the diffusers casting shade on 1 end but not the other.  That made me remember that is how it was kind of today.  My closest sensor had shade and the furthest one was lit up.  Well thank you for your input and keep me in mind for you B40 brother


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-19 00:39:09  

@pluric I just remember after every self "tune" I done that after break in the rifle mostly picked up speed.  But anyway she still drives tacks and it just had me semi stressing.  Why?  Well she IS the queen of my small stable.  Thanks brother

 


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-19 12:34:37  

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.

cross posted 


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scratchit
(@scratchit)
Joined: 2 years ago
Posts: 182
2020-02-19 14:42:19  

@josh3rd

 

do you shoot it regular?  How many rounds do you have down range since it was tuned?

i wouldn’t sweat it much unless you perceive it to be erratic.  Don’t get caught up in obsessing over chrono numbers.

 

...

 

...
 


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-19 20:57:08  

@scratchit I got about 3000-4000 rds now that I think of it.  I posted elsewhere that it was less but the more I think on it, i'm pretty sure. so yeah, about 6-8 tins give or take. as for shooting it regularly, I say 3x's a week

 


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scratchit
(@scratchit)
Joined: 2 years ago
Posts: 182
2020-02-20 08:14:18  

@josh3rd

 

I noted above that you stated the velocity as 785 FPS after having been tuned. I reckon that info was provided by the tuner. 

Now that you have your own speed-o-meter (thnx pluric or is that pluripotent), you’ve now established a “baseline” (about 765).  Go from there.  Don’t get caught up in the numbers.

 

Your numbers strike me as OK.  With any luck, your spring/piston seal is not quite middle aged IMO.

 

ATB.    How old are ya?, join thread.......

 


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-20 09:36:25  

@scratchit Hey brother, thank you for the feedback. As for age, i'm 44 but feel 64 and excuse me for my ignorance but what is ATB and join thread?

 


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scratchit
(@scratchit)
Joined: 2 years ago
Posts: 182
2020-02-20 09:42:14  

@josh3rd

 

ATB:  all the best ..... prob’ly picked up from the .bbs. (Of course that’s gonna generate its own set of questions)

 

Theres a running thread asking how old are you. A head count in a way.....

 

ATB

 

oh dear......moderated again

 

now when I look at the title of this thread, the irony overwhelms me

 


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-20 09:58:05  
Posted by: @scratchit

@josh3rd

 

ATB:  all the best ..... prob’ly picked up from the .bbs. (Of course that’s gonna generate its own set of questions)

 

Theres a running thread asking how old are you. A head count in a way.....

 

ATB

 

oh dear......moderated again

 

lol, thanks man.  


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MDriskill
(@mdriskill)
Joined: 2 years ago
Posts: 152
2020-02-23 07:31:47  

Percentage-wise, that’s actually quite a small difference, as others have said not really worth worrying about IMHO. Consistency over the string is more important to accuracy, and sounds like you are great there.

Mechanical wear is a possibility of course, but over the years I’ve found quite a few other variables that will produce minor changes in springer velocity readings: different pellet batch, ambient temperature, different chronys, shooting at a slight lateral or vertical angle over the sensors, state of the gun’s lubrication, and lastly how you hold the gun.

That last one I didn’t believe until I tried it myself LOL. If you pull the gun in tight against your shoulder you will consistently get slightly higher readings than with a loose “artillery” hold.


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josh3rd
(@josh3rd)
Joined: 2 years ago
Posts: 159
2020-02-23 13:37:29  

different batch of pellets?  thats crazy because i just opened a new tin different lot # but same brand/weight when i chronied and i feel that my angle to the chrono was skewed too


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MDriskill
(@mdriskill)
Joined: 2 years ago
Posts: 152
2020-02-23 15:12:52  

Not quite sure whether you are insulting me or agreeing with me, but my general point was that little things you might not usually think about can make small differences in velocity testing.

And I was assuming the tin of pellets you are now using, is not the same one used for the initial test two years ago.


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scratchit
(@scratchit)
Joined: 2 years ago
Posts: 182
2020-02-23 15:48:27  

@mdriskill

 

I think he’s truly incredulous!  At least that’s what I’m writing it off to.

 

Excellent thread folks.  I’ve thoroughly enjoyed it.

 

THANKS 

 


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