.25 34gr Pellets - How fast?

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Impact MK2 with .25x700 STX-A liner 1:27 Twist Rate, JSB MK2 34 gn, 50 or 100 M rings.
When you start with speed let say for example 860 fps and increase incrementally by 10 fps which I am considering medium steps...
Safe to say need 5 shots to stabilize the springs and Reg and a next 5 shots you measure the speed monitoring the POI.
In certain speed range you will see the group opens up for example 870 and about 885 the group shrinks and next 905 opens up and next 915 the group shrinks, and this happenes all the way at 950 or 960 and somewhere there all goes South ... These are fictional numbers I just mention it for pictorial.
When you start tuning don't be lazy, go with little increments little down and little up and watch your POI. Longest possible distance you can comfortably shoot.
To get a right tune that really satisfy sometimes needs several hundreds of shots, and a lot of air....
 
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Crown MK2 JSB 34 gr. 880 fps. I have owned about 7 .25 cal pcp rifles from the lower end Hatsan at44 to my current .25 pcp rifles the crown mk2 and impact m3 and they all shot best at speeds ranging from 860 - 900 fps. Going above 880 - 900 fps increases wind drift on diabolo pellets so if you dont want the extra FPE and you want the best wind drift stay as close to 880 fps as you can. I know it sounds weird and the first time I heard it explained years ago by someone who knows more than I do about drag stabilized projectiles I thought it wasnt true. Then I did what they said and checked in my ballistics app and sure enough above and below 880 fps with this particular pellet wind drift increases when comparing at 100 yds. 880 fps in my app gave the best wind drift numbers.
 
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LDP said:
Above and below 880 fps with this particular pellet wind drift increases when comparing at 100 yds. 880 fps in my app gave the best wind drift numbers.
Click to expand...


Interesting. I remember reading something that said the same, roughly around 880fps a typical dome has the least wind drift (highest BC)
However, when shooting out to longer ranges, like 100y, it is advantageous to shoot it a little faster, at the velocity sweet spot so to speak:
Because the wind drift increases as the pellet gets to much slower velocities further out — so the article recommended starting out a little higher than the ideal BC, say, 950fps or so.

Matthias


PS: Which ballistic app was it that gave you the result that at 100y with 880fps MV you had less wind drift than say, at 950fps?
 
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JungleShooter said:
However, when shooting out to longer ranges, like 100y, it is advantageous to shoot it a little faster, at the velocity sweet spot so to speak
Click to expand...
Yes I would say you would want to make sure you are using the best combination for the distance you shoot. If you stay at 50 yds and under the difference is so small you wouldnt care. If you are shooting to say 125 yds or trying for farther distance you would balance the speed around that as you said.

JungleShooter said:
Which ballistic app was it that gave you the result that at 100y with 880fps MV you had less wind drift than say, at 950fps?
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Strelok pro. I have a different app that I actually use for my rifles but I didnt want to mess around with my profiles or make new ones so I used my old profile in strelok. The only change in the data was velocity all other parameters stayed the same from one speed to the other.
 
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My P35 will only push JSB MkII 33.95 pellets to about 800 fps. I had to put on an aftermarket 35cc (bigger) plenum to get them going that fast. The barrel is 450mm long and the hammer spring can only open the regulated chamber when the regulator is set below 150 bar. But it is accurate at 800. It's my worst shooting P35 on the 30 yard challenge but I've shot a 194 with it. Gets about 40 shots/fill tuned this way. It's pretty short and only weighs about 5 lbs so I'm pretty happy with it but it is not a high powered 25. Powerful enough for me.
 
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In my Red Wolf with 1 in 17 twist poly, mediocre to poor accuracy below 890 at 50 and over but pushing them harder just got better till about 980... where the accuracy @ 100 seemed to plateau and going faster yielded nothing more but leaded barrel and more air use. At 1020, definitely started getting worse. Now stay aware that an important part of 100 yd plus accuracy is wind reading, so if it shoots well @ 25 but difficult to do well @ 100, could be wind sensitivity. Now I've posted quite a bit regarding this way back but do believe there are a couple of pellet/barrel anomalies... The 177 and 22 MRDS's come to mind here...
RTI suggested 1010 for MRD's with their long range barrel... a 1 in 30 twist, 6 groove. I can corroborate that it needs to be there or close.
Now for known reasons, I've found the Delta Wolf and Ghost peak around 940 ... again, 1 in 17 twist. We've been lead to believe that slower twist may be an answer to long range destabilization but in my samples, I've not seen conclusive evidence. I've compared slow and faster twist in the DW quite a bit but still can't say for sure, given pellet quality, barrel differences, and maybe day to day physical differences.
Now standard rifled barrels are a different thing... mostly I see best accuracy below 920, regardless of twist.
Ok, all that said... how does Mike N do it? Crazy stuff he posts 😉
Bob
 
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Dang... all the above was 22 cal, must have missed the 25 cal part...

I run them @ 900 n my Safari with 1 in 30, 5 groove poly. Going faster was ok but mainly used more air. Slower was ok also but more drop @ extended range. Friends have made a lot of noise about how good they are @ 975 but I've not seen it in my testing.
Bob
 
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