What kind of POI change to you get when changing the power?

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kmd1984

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Feb 20, 2016
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Utah, United States
Hi,

I have a FX Bobcat Mk2 in .25. It has a 2-way power selector on it. On full power (930 fps/25.4 gr), my 25 meter groups are pretty much one solid whole. However, when I switch to the lower power setting (650 fps/25.4 gr), my groups are not as tight as they are on full power, and the POI is about 1 MOA to the right?

Obviously, with less fps the pellets point of impact will be lower, compared to max power, but why are the groups less tight and why is the POI now to the right?

Any ideas?

Thanks,

Kmd

EDIT: I used to get 930 and 650. After having my gun "tuned" to be more efficient, I get 860/max, 620/mid and 465/low with JSB Exact Kings. With JSB Exact King Heavies Mk2 I get around 760/530/370.
 
The Smooth Twist barrels like to be shot at faster speeds.

It is the way it is designed when shooting JSB pellets.

If you want to shoot at lower speeds I suggest trying other

types and or brands of pellets.

Doesn't do that with the older FX guns using the Lothar Walther barrels

which shoot great at any speed and not pellet specific nor picky.

CA
 
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Coldair,

How did you know I am shooting JSB pellets? : ) I am going to try Benjamins and Polymag that I have lying around and see if that will make a difference.

Thanks for the input...

Kmd

P.s. I did not mention that I had the 2-way power adjuster wheel replaced with the 3-way one from the FX Indy. I did not think it was important. However, now that you are mentioning the fact that the pellets like to travel at faster speeds, I thought I bring it up. Especially considering that your "theory" now makes totally sense. I forgot at what speed the pellet travels at the lowest power setting, but the groupings are even worse! : )
 
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My Streamline used to do that. On lower power POI would be of course lower and to the left or right. I’m no barrel scientist but I believe it has to do with the interaction with the pellets speed and the smooth twist’s design. Have you cleaned your barrel lately? Might help?
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Interesting... Well, I just got it back from FX Airguns USA. They did a "service" on it, replacing a bunch of seals and what not. I would think that they cleaned it, but hey, you never know. Thanks for pointing that out.

Kmd
 
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 You could also try the Air Arms labeled pellets you may or may not have better luck because they are same but different.

In general I prefer the AA labeled versions because I had noticed more consistent results with those.

In some of the ST FXs I had, the AA shoot better at the lower power setting but not all and some are more accurate on high too.

I had fairly decent results with Barracudas and light weight FTTs and their 19-20 grain relabeled variants on low with some of them too.


CA
 
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You could also try the Air Arms labeled pellets you may or may not have better luck because they are same but different.

In general I prefer the AA labeled versions because I had noticed more consistent results with those.

In some of the ST FXs I had, the AA shoot better at the lower power setting but not all and some are more accurate on high too.

I had fairly decent results with Barracudas and light weight FTTs and their 19-20 grain relabeled variants on low with some of them too.


CA
Click to expand...

Also had great luck with the AA branded kings in .25 my Royale loves them.
 
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I love Air Arms Diabolo Field Pellets. When I got the gun, I bought a bunch of different pellets and went to an indoor 100 meter range. The Air Arms turned out to be the best (most accurate) of them all. However, the last time I ordered pellets, they did not have any AirArms, so decided to get some Benjamin and JSB's instead.

That said, the JSB's and Benjamins are not bad at all, but I will for sure get Air Arms next time. As a matter of fact, let me order some right now. : - )

Thanks for the input,

Kmd
 
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I think the consensus for the 25 gn JSB and FX ST barrel is that they like that 900+ speed range.650 fps sounds really slow for that pellet.

My Impact shoots MKII pellets best around 900 fps but my Cricket, with the LW barrel, likes them at 850-865. All pellets have their sweet spot.

As for the POI change to the right...could be ballistics at that low speed. Who knows. Rifle cant can cause a drift right or left at distance but not sure why a LOW setting that

s happening....sorry, not an expert....but I'm going with the ballistics hypothesis.

So, for accuracy, stick with your HI setting. For saving air and plinking cans...go LOW

KP
 
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I've had rifles shift left or right when switching pellets that got much better by re-crowning. Haven't always been able to see the crown discrepancy with a magnifier either. They really SHOULD just shoot lower or higher from the different speeds. I have only re-crowned if it was severe or accuracy was poor.

You can look at it with a magnifier and see how even it is.

Food for thought.....

Bob 
 
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I think the consensus for the 25 gn JSB and FX ST barrel is that they like that 900+ speed range.650 fps sounds really slow for that pellet.

My Impact shoots MKII pellets best around 900 fps but my Cricket, with the LW barrel, likes them at 850-865. All pellets have their sweet spot.

As for the POI change to the right...could be ballistics at that low speed. Who knows. Rifle cant can cause a drift right or left at distance but not sure why a LOW setting that

s happening....sorry, not an expert....but I'm going with the ballistics hypothesis.

So, for accuracy, stick with your HI setting. For saving air and plinking cans...go LOW

KP
Click to expand...


Good points. Thanks for the input...

Kmd
 
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I've had rifles shift left or right when switching pellets that got much better by re-crowning. Haven't always been able to see the crown discrepancy with a magnifier either. They really SHOULD just shoot lower or higher from the different speeds. I have only re-crowned if it was severe or accuracy was poor.

You can look at it with a magnifier and see how even it is.

Food for thought.....

Bob
Click to expand...


Bob,

I have no idea what you are talking about, ha ha. However, I just did a quick google search to find out what it is, and I am going to look into it. Thanks for pointing that out.

Kmd.
 
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I guess every gun/barrel is different, my Bobcat Mk2 shoots JSB Kings "lights out" on high or low power, 925/660 fps, low power groups just dead low a few inches, I never changed factory settings and I never will, The best freehand group I ever shot in my life (sitting) was shot with my Bobcat Mk2 .25 on low power. The groups pictured is high/low power from sitting position at 48yds. Group on bottom is high power, (more than 5 shots) top group is on low power 5 shots. The distance between these group is NOT the POI difference, left is up, I didn't plan to post these groups, 15 clicks is about the difference but no L/R shift, call it four inches..
1541595569_19302129545be2e1b14494f6.72473297_bobcat high low.jpg

 
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I've always thought the better way to lower speed/power is by changing HST, if you just change how much air goes into the barrel (transfer port size adjustment) are you saving as much air ?

I could be totally wrong but changing how much air is used out of the plenum should be more efficient and quieter.
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Maybe!? I know to little (nothing actually, ha ha) about tuning/adjusting hammer springs, and stuff like that, so I have to fall back onto the good old power adjuster. The Bobcat Mk2 in .25 has normally a 2-way installed, but I had it replaced with a 3-way. : - )

Thanks,

Kmd
 
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With the Streamline, the only adjustment you can make externally is the power wheel (transfer port). It does save air somehow....I get 55 shots on High, 70+ on Mid and 100+ on Low.

On my Ultimate Sporter it's the same type of adjustment but no air savings.

The power wheel comes in handy when shooting outside, then inside then back outside.
Click to expand...

I get +/- 99 shots on Full power. I started out on 225 bar and it went down to 150 bar. I was able to shoot 8 magazines, each holding 11 rounds. Since my reg is set to 140, and each mag made the pressure drop by 10 bar, I believe it is safe to say I get at least 99 shots on full power, and regulated. I did not have a chance to test mid and low power yet.

I agree. Being able to switch power by simply turning a know on the outside of the gun is a huge plus for me.

Thanks,

Kmd
 
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