Question to long range shooters - what pellets are the best BC in .25?

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bigHUN

bigHUN

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Jan 16, 2020
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L4G7X4 Canada
FX Impact .25 MK2 PP, 700 mm Superior Heavy liner (just switched out recently from STX-A).
Liner indexing done and currently entertaining with barrel harmonics tuner, as much the weather allows.
I am weight sorting my pellets, washing and lubing, so the manual work - both the effort and time is invested deeply, I still need to figure some testing tricks how to predict the occasional fliers. If, this just possible anyhow.
In past several months over summer I was shooting JSB 34gr King Heavy MK2's and discovered some inconsistencies with these MK2 pellet skirts, I assume again this can lead to internal friction inconsistencies and this can lead to ..... a whole new chain reaction.
For these above reasons I switched out the liner and started buying slugs, currently shooting ZAN 37 grain and next is to test the ZAN 41 grains. The results I am seeing @ 100 promising. The POI grouping from average 1-3/4" with 34gr pellets (860-890 fps), shrink to about 1" with 37gr slugs (920-940 fps).
But my plan is to train and prepare for next year competition season so again sooner or later I will be "forced" getting back to using pellets, and over the winter I shall prepare a larger stock.
What is the experience with .25 that can be successfully used for long range scoring? Investing into .30 equipment doesn't look feasible at the moment.
 
The 33.95 originals were the best BC in the .25 but as already mentioned, they quit making the originals and now only offer the 33.95 MKII. You may still be able to find some of the originals somewhere, but it’s going to be tough. Most people that have the originals aren’t going to let them go either! 😉 The BC of the originals wasn’t a huge difference over the MKII’s but they also were more accurate for many people, in a variety of air guns. It’s a real bummer for a lot of us that they aren’t being made anymore. Why JSB is throwing the MKII’s in the original’s tin and selling them that way is a mystery but quite a few of us have looked into it thoroughly and the originals aren’t being made anymore. Maybe, hopefully, they’ll resume production again in the future??? 

Stoti
 
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I have seen some of you visiting nolimits post a while back... I trust that there is a big potential for errors in POI from the pellet body run-out, did you had a chance to proof yay-or-nay the possible fliers sorting out pellets that way?

I have only one BR ready gun and I lost my patience-tolarance-comfort quick swapping and detuning between slugs and pellets, shooting now slugs until the box of 1K batch lasts (and btw just checked no JSB MK2's currently at my dealers).
 
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Some of their BCs are accurate, some aren’t. For example, they list the .22 JSB RDM but the test velocity is only 718 FPS. So of course their listed BC is very low. This isn’t the only example where they do this. I’ve recommended to them in the past to test their pellets and slugs at commonly used speeds… Just another reason to do your own BC measurements with your barrel. 
 
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Some of their BCs are accurate, some aren’t. For example, they list the .22 JSB RDM but the test velocity is only 718 FPS. So of course their listed BC is very low. This isn’t the only example where they do this. I’ve recommended to them in the past to test their pellets and slugs at commonly used speeds… Just another reason to do your own BC measurements with your barrel.
Click to expand...

What is the math for working up BC?
 
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At my place currently no JSB pellets available in projected next 5-7 weeks, so that means shooting slugs probably up the end of this year. I still have one tin of sorted-ready to go MK2's but I put it aside for a case of emergency :)

For now ZAN 37 and 41 grain, but I don't think slugs are officially approved for BR competition (at least this what I know about) so I planning pellets for next year/season only.
 
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Some of their BCs are accurate, some aren’t. For example, they list the .22 JSB RDM but the test velocity is only 718 FPS. So of course their listed BC is very low. This isn’t the only example where they do this. I’ve recommended to them in the past to test their pellets and slugs at commonly used speeds… Just another reason to do your own BC measurements with your barrel.
Click to expand...

What is the math for working up BC?
Click to expand...

😂
 
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Some of their BCs are accurate, some aren’t. For example, they list the .22 JSB RDM but the test velocity is only 718 FPS. So of course their listed BC is very low. This isn’t the only example where they do this. I’ve recommended to them in the past to test their pellets and slugs at commonly used speeds… Just another reason to do your own BC measurements with your barrel.
Click to expand...

What is the math for working up BC?
Click to expand...

I think what center-cut is suggesting, is measuring your pellets velocity at two different points and using a ballistics program like chairgun or strelok to calculate the BC.

https://en.wikipedia.org/wiki/Ballistic_coefficient

This is a correction.

I made the assertion here that you couldn't calculate the ballistics coefficient and that assertion is not correct. The way that we use the term ballistic coefficient in small-arms calculations isn't precisely the way that physicists use it their equations. That Wikipedia link will tell you more than you ever wanted to know about it.

The assertion that we must measure ballistics coefficient in our application is essentially true because we're using it to define a relationship with a standard model. When you don't have a standard model you've got to calculate it.

Edit: Tit for tat unnecessary... stricken below. My apologies. I should not allow myself to be baited, but I do... :(

Perhaps Franklink or someone else equally brilliant, say a "nuclear engineer", will dine to explain to us how that math works.




 
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Beside the fact I have a porting mod in the MK2 PP (slotted the transfer hole also enlarged the valve + poppet),

speed is more then plenty with JSB 34gr pellets, but the 37 gr slugs still feels a bit hungry for more speed, currently sub 960 fps @ 145 bars. I am not saying underpowered, but if I would want to jump to heavier like 40-45 gr slugs I assume the power maybe on borderline.

Would (or could) be a larger 720 mc plenum a vise investment?
 
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