FX Acceptable FPS spread

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Cotton-Eye

Cotton-Eye

Member
Jul 5, 2023
28
11
United States
Hi All, I’m new here and new to the world of “real” high power air rifles. I’ve had a Benjamin Marauder that I’ve been using for a few years And just picked up an FX Impact M3 .25 cal 700mm. I had an issue that I resolved with the help of FX customer service following a master class on YouTube. I basically had to pull the entire rifle apart and put it back together. I’ve got it driving tacks again but my chrono is showing spreads averaging around 5 fps but as much as 10 fps with some shots even more. Is this typical or should I not have spreads that high? I found a couple YouTube videos on adjusting the valve rod a certain distance out from the rifle (by tightening c52 in correct position) but it was after I already put the rifle back together. I had c52 screwed in as far as it would go.

Any advice for this noob on how to tune the rifle to tighten up the spread? Harmonic tuner perhaps?

1st reg is between 145 and 148

2nd reg at 115

power wheel at 16

micro adjuster a hair under 4

valve fully open? (beyond line 4)

shooting FX 34 gr pellets and FX Atomic 26.6 gr pellets

Thank you all in advance!
 
Where it jumps to the 900’s is where I switched to the atomics…

Shot count: 80
Low: 861
Hi: 967
Avg: 904
Spread: 106
STD Dev: 38.9
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I never even think about those numbers. They are meaningless if your gun isn’t accurate. When you find the accuracy you’re looking for, those numbers will be what they are. And they will generally be good depending on the projectile used. Don’t worry about it unless it’s really big or erratic. I just had a first shot 33.95gr pellet at 918fps and the next three shots between 898-907fps all cut the same hole at 75 yards yesterday. My gun obviously wasn’t concerned with the ES.
 
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Vetmx said:
I never even think about those numbers. They are meaningless if your gun isn’t accurate. When you find the accuracy you’re looking for, those numbers will be what they are. And they will generally be good depending on the projectile used. Don’t worry about it unless it’s really big or erratic. I just had a first shot 33.95gr pellet at 918fps and the next three shots between 898-907fps all cut the same hole at 75 yards yesterday. My gun obviously wasn’t concerned with the ES.
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Totally agree. Unless ES is extreme, or you're shooting near the end of the rifle's absolute maximum practical range, it isn't a significant factor.
 
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Vetmx said:
I never even think about those numbers. They are meaningless if your gun isn’t accurate. When you find the accuracy you’re looking for, those numbers will be what they are. And they will generally be good depending on the projectile used. Don’t worry about it unless it’s really big or erratic. I just had a first shot 33.95gr pellet at 918fps and the next three shots between 898-907fps all cut the same hole at 75 yards yesterday. My gun obviously wasn’t concerned with the ES.
Click to expand...

Yep, I’d agree with Vetmex - find the velocity that your rifle is most accurate with that pellet. Don’t worry about spread - if accurate the spread will be reasonable.

Cotton-Eyes 55 shot string is basically between 870-888fps - with 3 shots in the low 860s likely due to out-of-spec pellets.

18fps spread over 55 shots seems reasonable to me - should not effect accuracy if the pellet chosen works well at 880fps.
 
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A way of understanding a reasonable spread is: if you are shooting 900fps, and your ES is 15 your deviation is <2%
If your SD is 9 you are at 1%. These are hypothetical as l figure but it helps you to understand. My Mav is 912 fps.
ES 7. SD 4. About all I can ask. Less than 1/2% . That's with 700 barrel , with compact barrel, I shoot considerable slower @ 847.same percentage of deviation
 
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id like to see a couple strings with the power wheel on 15 - 14 - 13.

and you said the micro was a hair under 4,
and thats the number that really matters.

because both the power wheel & the micro adjust the same thing (hammer spring tension)
but in different increments.

when i setup my m3 my spreads would be larger if i had too much hammer spring.

good way to tune the m3,

put the micro up past 4 and the valve adjust out past the 4th line,
start turning down the micro till your velocity drops 10-20fps,
then slowly start turning the valve adjust in till velocity just starts to drop a little more.

i get usually no more than a 1 or 2 fps deviation out of my m3,
yours can absolutely do better than it is (y)
 
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On the other end of the spectrum you can also have the tightest of spreads and not have the accuracy you seek.
During accuracy testing one day I shot thru 36 shots and had a 2 FPS spread, continued on and after 96 shots had a spread of 14. I was still dissatisfied as I was not where I wanted to be accuracy wise, so piggybacking on what VETMX told you, seek accuracy first then worry about spreads later.

And by the way, those tight spreads came with sorted and weighed pellets. So if you’re hung up on tight, really tight, spreads, be prepared to take on the task of sorting.

My accuracy for bench shooting was eventually found, by finding the right speeds in combination with not over working the gun, in case you wanted to know
 
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