RAW .25 cal, JSB Heavy (33.95 grain) BC, Measured (Polygon Barrel)

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SMH77

SMH77

Member
Oct 28, 2017
997
72
Wisconsin, United States
Just as a PSA, I figured I’d share with you the results of my measurement today of the BC of a JSB .25 cal 'Heavy' (33.95 grain) pellet, shot through a RAW LW polygon barrel. First, it was very cold outside (16.5F, 30.25 " Hg pressure, falling, and lightly snowing), so I adjusted the environmental settings to match in Hawke's Chairgon Pro program (Mac version).Pellets were NOT measured and just randomly grabbed from a new tin of the 'non-Mark II' (original) pellets.
Muzzle velocity averaged (~ 6 inches from muzzle): 897 fps
Distance to far measurement: 43.8 yards
Velocity measured at 43.8 yards averaged: 759.3 fps. I opened up Chairgun (Mac version) and adjusted the environmental conditions, temp, etc. I then went to the BC calculator app, plugged in the above data, and it calculated a BC for the pellet of 0.0444. Seems to be right in the ballpark of other readings that have been reported. As stated above, the barrel used was a RAW .25 cal polygon barrel, made by Lothar Walther specifically for RAW (no idea of the twist rate).Notes: same chrony was used at both distances. Velocities were held super tightly (muzzle was: 899.2, 894.8, 897.6, 894.9, 899.1, 893.8, 899.4 fps; 43.8 yards measured 758.1, 760.1, 758.9, 757.8, 754.8, 762.5, 762.9 fps). Average of 7 shots each were used, gun was refilled between shooting near and far. So, in conclusion, the JSB ‘Heavies’, in .25 cal (33.95 grain), shot through my RAW with LW polygon barrel at 43.8 yards had a BC of 0.0444. Hope this is helpful for anyone looking for data from this gun / setup?
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Edit: Sorry, I had my distances measured sligthly differently, but was shooting from the same spot, so the original BC reported was tweaked slightly. I've corrected them above now.

Sean
 
Man Sean, thanks for taking one for the team. It was sunny and 70 yesterday and the same today. Looks like I could have done the same but I did do it on my Wildcat instead. My muzzle velocities were very consistent but my velocities at 60yds were all over the place. Must have been the shade of the tree giving me bad reading. Just for grins I'll try my RAW and use 50yds as my secondary point since it is in the sunshine. I'll report back later. Thanks for motivating (guilting) me, lol
jk
 
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Got off my butt and checked the BC of my RAW HM1000X 25cal. Here's what I came up with. I plugged 70 degrees F, 11% humidity, 3600' elevation, Far chrony distance was 49.0 yards, close chrony distance 1' from muzzle. which made the distance between the two 48.66yds. I'm shooting weight sorted heavies with the skirts sized to .252".
My muzzle velocities in the shade using the light kit
886
886
885
887
882
886
888
avg
885.7
My velocities at 48.6yds using the sunlight at the chrony
797
794
801
794
avg
796.5
My BC came out at .0521 which sounds high. The only thing that I can think of is the difference in using the light kit on the chrony versus daylight readings. It was too late in the evening to just use sunlight at the muzzle due to shade cast by a storage building where my bench is. I'll try it again with the same light source.
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Good information there jking. Thanks for sharing.

A couple of comments: first, it's simply just 'not right' that you've been shooting in 70F temps while I'm freezing in the snow, LOL. Sertiously though: I love the snow-I just wish going inside where I filled at 220 bar didn't drop my pressure (and shot count) so dramatically when the temp stabilized outside. Oh well, I plan to redo this when the temps increase a bit anyway...

Regarding your BC measurement: yeah, it does seem a bit high-I suspect it has something to do with the light source differences. For me, I used the same chrony, with the 'v bars' extended upward, but did not use the diffusers on top, since it's overcast today (didn't need them). Chrony was setup the same way both at the muzzle, and at the far target. I had consistent lighting, and temps throughout the test.

I have heard that the BC's from FX barrels (with the ST setup) are 'shifted' from normal rifled barrels (and possibly polygon barrels-this one was an unknown to me as to how it affects the numbers). I don't recall if FX barrel yield a higher or lower BC compared to a LW, BSA, etc. barrel. In fact, this is the whole reason I started a post a while back specifically asking for BC's through a polygon barrel. Ham's DB reflects the BC's that he obtained from a FX Impact barrel, so I expected them to be different than mine. However, they aren't looking too terribly different when I compare my reading of 0.0444 to his of 0.046 for the same pellet. Do you have the BC's from your Wildcat for the same pellet? Perhaps you can test both guns over the same setup (RAW and Wildcat) when you do it again? I would be curious to see how they are, or aren't, different.

Lastly, I had to go back and edit my original post-mainly because I realized (after the first post) that I had measured the distance to target differently when I reported the .30 cal JSB light results, vs the results in this thread (I do intend to compare them, as they're from the same gun, at the same settings, but different calibers installed). The first report (43.8 yards) was from the area of the breach from the first set of measurements, and I mistakenly used the distance from the end of the moderator for the initial posting today (43.1 yards). So I revised the results to reflect the same distance, since I was in the same place, and the target was also in the exact same place for the two tests. I did note that the BC calculation was a bit different when I adjusted the distance-even from 43.1 to 43.8 yards-so it really is pretty sensitive to having an accurate distance measurement. Yep, I totally get the ensuing discussion about 'the distance should have been from the muzzle...'. I won't debate that point-although I've thought about that a lot and thought "when out in the woods, rangefinding a target, I do it from where I'm standing and then shoot-so that's technically not the correct distance, etc..." But I digress-I made them the same for comparison sake.

I do plan to repeat-and perhaps even swap barrels the same day as well-to do a better comparison in the future. I want to measure the BCs from .25 cal JSB light, JSB Heavies, Barracuda's, and Barracuda Hunter Extremes (and maybe Polymags too). In .30 cal I mainly want to compare the JSB light and heavy pellets-and then review all the data against itself to understand pellet selection for my own purposes.

Please do post again once you've tried the lighting such that it's consistent at both locations. Overall, I think this is really good stuff, and hopefully it will help build the collective group's knowledge, etc.


Sean
 
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I was just reading a bit in Ryan Cleckner’s book (‘Long Range Shooting Handbook’ at the end of chapter 9, the summary view on BC’s) that environmental factors DO impact the BC measurement. So it IS possible that your BC numbers are higher due to the more ideal conditions you were measurement in, compared to mine. This makes sense to me as well because thicker, more dense air will slow the pellet down faster than warmer, less dense air. I see this when cycling too: for the same wattage in 90F temp, I could be riding at 19 mph, or 14 mph based on the air density due to the change in temperature.

Question: is your .25 caliber barrel a polygon barrel like mine is? I think I recall that it is, but wanted to confirm. If so, and you confirm the readings weren’t biased based on the sunlight affecting your chrony, then you and I may have, collectively shown the range of variation of the BC for this pellet, through the same barrel-that is good info to know as well. We could do likewise for other pellets too as a community service for others.

Sean
 
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"jking"Could have something to do with it. I also remember having a little tail wind, maybe 5mph or so. Super dry air at 11% humidity yesterday. I'll check it again in a few days and rule out the chrony light source effect. Yes, my barrel is the polygon.
jk
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That's good to know. Ok, perhaps a dumb question, but I'll ask it anyway: Where was the distance measured from-at the muzzle of the gun, or from the breech (effectively, where you were seated when shooting)? I just want to be consistent as the little bit of difference does have an impact on the calculation results for BC.
 
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Update: I am in the process of ‘re-acquiring’ my .25 cal LW (non-Polygon) barrel I’m the next week or two. I am thinking about doing a BC comparison between the two barrels, holding everything else constant when it arrives. I am also planning to map BC across temps over the coming year, since Strelok Pro allows multiple BC’s per temp for a projectile. Just wanted to throw that out there in case anyone’s interested in seeing the data later.


Sean
 
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"SMH77"
"AirSupply"You might find this old tread interesting. Not specifically the polygon barrel. This is where Ted started using the King Heavys. He then went on to win EBR with that pellet. 
Michael
http://www.airgunnation.com/topic/jsb-new-heavy-25-cal-kings-100-yards-half-inch-group-and-normal-kings-group/
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Thanks for the info and the link to the post-I’ll take a look. I appreciate the heads up.
Sean
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Man i realy wish i could see the figures from Harry’s posts-so much good info there that it’s a shame to not see the figures he’s providing. Any way to locate the figures?
 
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I tried finding the BC of my RAW shooting the MKI Heavies again. This time around I used my unlighted chrony at both ends. The environmental conditions were 63*, 3622 elevation, 20% humidity, 30.13 inch and rising.
49.0yds, 886 average over five shots 1' from the muzzle, 785 average over 3 shots at the chrony.
This time I came up with a .0543.
When setting up the environmental conditions I couldn't get the above values to stay correct in their corresponding boxes in Chairgun. Even after the hitting the reset button the barometric press, elevation and humity would change on me when I moved the cursor away from that point. I would be great is someone else could plug my numbers in and see what you get.
0def6fa6947c0712995df6ff14bd6496.jpg
 
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"jking"I tried finding the BC of my RAW shooting the MKI Heavies again. This time around I used my unlighted chrony at both ends. The environmental conditions were 63*, 3622 elevation, 20% humidity, 30.13 inch and rising.
49.0yds, 886 average over five shots 1' from the muzzle, 785 average over 3 shots at the chrony.
This time I came up with a .0543.
When setting up the environmental conditions I couldn't get the above values to stay correct in their corresponding boxes in Chairgun. Even after the hitting the reset button the barometric press, elevation and humity would change on me when I moved the cursor away from that point. I would be great is someone else could plug my numbers in and see what you get.
0def6fa6947c0712995df6ff14bd6496.jpg
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Just saw this now-thanks for retesting this for us. I appreciate the efforts. I am without a scope until Monday (as I just sold my scope and am switching to an Athlon scope) so I can't retest at the moment, despite nicer weather (going to be over 20F tomorrow, yeah!!!) finally on its way.

A few comments: over the last couple days I've read quite a few posts from Yrrah (Harry) and note one of the things he showed in his testing-the BC seems to rise more the further the distance he tested over (he has some theories about the pellet stabilizing as it leaves the muzzle, etc). This may be part of the reason that accounts for why your BC is higher than mine. Also, the BC's he reported are not too different than what you have measured for the king heavies. He was testing down in Australia so the weather was likely closer to your temps compared to mine, LOL. Thanks for retesting-I actually do believe your numbers are accurate.

Once I have a scope back on my gun, I'll put it through the paces and retest the BC-and will do it at a similar distance to yours.

Can you be very specific for me (so I can be consistent with your method): was the distance measured from the muzzle to the front sensor of the chrony, or some other way? I was setup my next BC test measuring the same way as you.

Lastly, it seems to me I had to disable the 'elevation' part of the environmental conditions in order to get the pressure to reflect the local pressure when tested (otherwise it was trying to force my elevation to be below sea level). What version of Chairgun were you using-the iPhone app, Mac version, or something different?


Sean
 
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First off, thanks Airsupply for checking my numbers. Were you able to use the environmental conditions with the program you used?
Sean, I've seen some of Harry's work and he's really precise on his results and reports. To answer your questions, The measured distance was from the end of the muzzle to the first sensor on the chrony. Then I shot the distance ( Nikon range finder) from the where the chrony was (1' from the muzzle) to the chrony's new position at 49.0yds, also to the front sensor. I used a cement cinder block set up beside the chrony to get a solid range on.

On the Chairgun issue, I'm using the PC version of Chairgun Pro 4.2.
Hope it warms up for you Sean
jk
 
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Guys,

You are pointing out the things that make air gunning great, everything changes, all the time. We tune for one instance and it changes when we fire the gun. The BC changes at different distances and between other distances. If you had a crony at 25 yds, 50, 75 and 100 yds you would get 4 different readings. If you went between each marker and another you would get additional different numbers. Air guns are getting more accurate and we each, in our own way, want to improve upon what we have. Now we can shoot pellet on pellet at 100 yds( the gun can, maybe we can't), soon the guns will be able to do that at 150+ yds, if not more. We are in for a great ride, let's enjoy it.
 
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