GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: rsterne on December 12, 2019, 01:32:16 PM
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HAM published their first test of the new 22 gr. FX Hybrid Slugs today, in a comparison test to the 16 gr. FX Diabolo pellet.... See Reply #49 for revised data....
https://hardairmagazine.com/reviews/shooting-fx-slugs-and-pellets-in-an-impact/
You can read through that for the details of the comparison, but I gleaned one very important piece of information from it.... They had the muzzle velocity (860.5 fps) and that at 50 yards (772.5 fps), so using ChairGun I was able to calculate the BC.... I assumed the typical temperature (77*F) and humidity (70%) stated on the HAM website, and used the altitude they gave of 244 ft.... and further assumed standard barometric pressure, since those numbers were not given in this test.... I used the G1 drag model as being the most suited to this shape of slug, and calculated a BC of 0.062 0.071.... When HAM publish their BC for this slug, it may differ slightly because of the actual conditions during the test....
The SD of this slug is 0.067, so a BC of 0.062 0.071, works out to a Form Factor of 1.08 0.94.... not too surprising for a flat based slug of these proportions.... Anyways, for those of you who were wondering about the BC of these new slugs, we have our first independent piece of data for the 22 gr.... We can expect the heavier FX Hybrid slugs to have a better BC, roughly in proportion to their weight....
Bob
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Bob do you recall what the marketing package gives as a BC?
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I haven't seen anything on the packaging.... However, I have seen claims of a BC of 0.080.... The Hybrid slugs are going to be available in different weights, perhaps that was for a heavier one?....
Bob
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This is the rear of the packaging on the 22gr .22 Hybrids.
(https://i.ibb.co/7pdmQRQ/Screenshot-20191212-172058.png)
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So how much of a variation is that?
Is that in the noise or a significant difference?
I have 500 rounds of NSA 30 Cal waiting for my raptor but that is as close as I have some to slugs yet
Lots to learn!
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They are claiming .08 for the hybrids. I'm no expert, but I'm pretty sure they're nowhere near that. When Nick's hollowpoints that are very similar state the same BC, but the hybrids have a way bigger hollowpoint and a super dished base...
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I didn't see that BC of 0.080 on the bottom of the package.... IMO, that is enough difference that it is outside normal variation.... However, since there is no standard way of testing BC, nor velocity, it is possible that in some guns, at some velocities, that could be correct.... The BC calculated from the HAM tests could vary a bit, depending on the atmospheric conditions of the day as well.... Nick claims the same BC = 0.080 for his 23 gr., which are a lot shorter (but a grain heavier)…. The 22 gr. FX slug is nearly as long as Nicks 27.5 gr. slug (which he states is BC 0.090)….
The only way to know what the BC is in YOUR gun at YOUR velocity is would be to test it yourself.... unless we get a LOT more data.... The cavities inside the slug, and the hollow base, should make no difference to the BC.... All that matters is the outside shape and the SD (weight)….
Bob
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The cavities inside the slug, and the hollow base, should make no difference to the BC.... All that matters is the outside shape and the SD (weight)….
Bob
Bob, thanks for this. Looks like I need to do some more reading on BC. I thought hollowpoints made BC lower.
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There is no difference in drag (FF) when comparing them to the same shape FN bullet (same Meplat diameter)…. the air in the HP travels with the slug, so they are effectively the same shape.... However, since they are lighter, the SD is lower, and hence the BC is as well.... but only because of the weight....
BC = SD / FF
Bob
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I might have missed accuracy testing with the hybrid slug? Or at least, shooting them at paper at 50 yards?
The reason why I ask, is that the smooth twist barrel has a very slow effective twist rate, and is unlikely to stabilize anything other than diabolo pellets out to 50 yards. If the slugs were yawing or tumbling, their BC would suffer badly. That could explain the 0.08 VS 0.06 BC question.
Shots on paper, showing round or key holes with the slugs would be the clue...
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Regardless of the actual BC, it will:
A: be greater than conventional diabolo-style pellet
B: further prove we are in the Golden Era of PCPs- the fact we have manufacturers really exploring common-sales slugs and hybrid slugs makes this an exciting time
With my intention of getting a Korean cannon (Eagle Claw or the Sumatra) in .22, I'm following this thread closely for the grins- and hybrid slugs seem like a perfect projectile for what ails me
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Personally I do not see any reason to use slugs under 50yd if it is just not really windy weather. Exact ballistic I am obviously adjusting by iteration in chair gun . I am changing BC until it fit real ballistic line at 33m/66m/99m.
It is really nice to see all works whit relatively new idea – developing slugs/bullets for PCP AGs.
I want to see testing of FX hybrid slugs at 100 yd.
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There is no difference in drag (FF) when comparing them to the same shape FN bullet (same Meplat diameter)…. the air in the HP travels with the slug, so they are effectively the same shape.... However, since they are lighter, the SD is lower, and hence the BC is as well.... but only because of the weight....
BC = SD / FF
Bob
Next importent notice.
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Personally I do not see any reason to use slugs under 50yd if it is just not really windy weather.
The reason could be because you have been shooting them at 100 yards, and a sub 50 yard target presented itself.
Dubber and his mates in SA shoot pest birds from 25 to 150 yards. They appreciate the extreme expansion of hollow point slugs; and the hybrids in particular. In the US, similar results could be achieved by shooting regular .30 pellets because there is no caliber restriction. SA is limited to .22; so those guys want the best performance they can get in .22.
Certainly, many people are going to ask themselves if their application justifies the cost of the FX hybrid slugs. I am starting to ask that about regular pellets, over .177 caliber :)
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This is the rear of the packaging on the 22gr .22 Hybrids.
(https://i.ibb.co/7pdmQRQ/Screenshot-20191212-172058.png)
Dayuummmm!!! I need to get me some of dem FX slugs.....they shoot flatter than my 220 Swift.
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This is the rear of the packaging on the 22gr .22 Hybrids.
(https://i.ibb.co/7pdmQRQ/Screenshot-20191212-172058.png)
Dayuummmm!!! I need to get me some of dem FX slugs.....they shoot flatter than my 220 Swift.
Lol I just realized the "trajectory comparison" on the back. VERY exaggerated ::)
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This is the rear of the packaging on the 22gr .22 Hybrids.
(https://i.ibb.co/7pdmQRQ/Screenshot-20191212-172058.png)
Dayuummmm!!! I need to get me some of dem FX slugs.....they shoot flatter than my 220 Swift.
Lol I just realized the "trajectory comparison" on the back. VERY exaggerated ::)
Dillon, didn't your hear that they're unaffected by gravity. At least that's what I heard on a YouTube video. Those Swedish engineers figured it out. Truly, FX is at the forefront of slug and Airgun development.
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Lol I just realized the "trajectory comparison" on the back. VERY exaggerated ::)
Especially when you consider that the MAIN component in trajectory is the VELOCITY.... The BC only plays a minor part, and if the slug is heavier than the pellet you used previously....
well you get the point.... ::)
Bob
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Hey Bob what about wind? What is the biggest component of that and how does BC play in?
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Wind drift is absolutely dominated by the effect of the BC.... roughly speaking it is inversely proportional.... double the BC, half the drift.... Velocity plays a relatively minor part, and in fact the drift increases above about 850-900 fps, even for slugs.... with a huge increase in wind drift in the Transonic range (Mach 0.8-1.2)…. Believe it or not, for a given slug, you would have to drive it between 2500-3000 fps to get the drift down to as low as it is at just 900.... That is one thing airguns really have going for them…. we operate right in the sweet spot for wind drift.... 8)
Bob
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I love this place
What causes wind drift to increase at that 950-1200 FPS?
In a slug ?
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I love this place
What causes wind drift to increase at that 950-1200 FPS?
In a slug ?
Bob will probably spank me with his answer, but I would guess that at over 1000fps, you are approaching/treading in Transonic range. Weird things happen there and anywhere near there. ;)
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What causes wind drift to increase at that 950-1200 FPS?
In a slug ?
The BC drops and does not fully recover until you reach Mach 2...
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why?....what does that look like in slugs? I know this is a huge issue with pellets....but though slugs and twists would help?
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It has to do with the formation, shape and position of the shock wave at different projectile velocities.
https://www.youtube.com/watch?v=BPwdlEgLn5Q (https://www.youtube.com/watch?v=BPwdlEgLn5Q)
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hence the need for air strippers?
Just double checking my understanding.....I love this place!
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hence the need for air strippers?
Just double checking my understanding.....I love this place!
I'm not sure air strippers do all that much at lower velocities. Maybe they do, but I am the biggest variable when I shoot. :o ::) ;D ;)
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well I sure understand and live that every shot!
+1 LOL
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Air strippers reduce muzzle pressure and the tendency for the projectile to be buffeted directly after it leaves the muzzle. The effectiveness of a stripper is related to how low the air pressure is on the back of the projectile, and how little air flows over it from behind just after it leaves the end of the barrel; not on the speed of the projectile.
Diabolo pellets benefit more from an air stripper because they are nose heavy and drag stabilized. Muzzle blast actually tries to flip the pellet over for an instant. The benefit still exists for slugs, but buffeting has less effect on a slug due to its shape and its rear biased center of gravity.
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I'm not sure air strippers do all that much at lower velocities.
It is not the velocity that matters, but the muzzle pressure.
Now, with high velocity, you often have high residual muzzle pressure; so in that sense, more powerful airguns tend to have air strippers.
Short barrel airguns at moderate velocities will also benefit from them because they have higher muzzle pressures than if their barrels were longer.
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https://www.youtube.com/watch?v=j493HvCkMbM (https://www.youtube.com/watch?v=j493HvCkMbM)
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Man I may want to retake my high school math classes again....with this type of relevancy I think I would Pass them!
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I'm not sure air strippers do all that much at lower velocities.
It is not the velocity that matters, but the muzzle pressure.
Now, with high velocity, you often have high residual muzzle pressure; so in that sense, more powerful airguns tend to have air strippers.
Short barrel airguns at moderate velocities will also benefit from them because they have higher muzzle pressures than if their barrels were longer.
Yes, I should have included pressure, but lower velocities *usually* mean lower pressure in AGs. Not always, but a lot of the time. ;) :D ??? ::) 8)
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Good description
https://sites.google.com/site/technicalarchery/technical-discussions-1/drag-coefficients-of-bullets-arrows-and-spears
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My Chairgun stopped working or I would do this myself. I'd love to see a basic drop chart comparing the FX slug to the FX pellet since we have the data. Curious how much flatter it really shoots.
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18gr JSB Jumbo Heavy/BC=0,03 vs. 18gr/22gr FX hybrid slug/BC=0,062 at 950 FPS
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So far, every time I've tested pellets or slugs,the BC works out WOSE at short range than it does when tested at longer ranges.
(this would by by 2 chronographs, measured from the muzzle to the middle of the chonograph for each).
So the BC numbers for something like 10 to 30 yards is always lower than the BC for 30-60 yards.
Without the radar type crono, it's all I had. "Had" rather than "have". YOu'd likly have guessed that at long range, killing the far chrongraph is a likely event.
Bob will likely tell you why they sluff off velocity faster in the first couple of yards.....I'm just going to assume that faster (closer) and the little "wiggle"many projectiles have at the muzzle is part of it.
The practical side thinks that if you are measuring BC at close range...they you are really just gathering random data. If it's short range,then the BC really isn't all that important for anything you are actually doing; what high BC slugs do well isn't up close.
.06-.08 is still a BC about 2X better than the good pellet-pellets. Not that it really makes a rats-rump of differnce at short range. Nothing I've shot at 25-30 yards with a lower BC 34gr. pellet-pellet would have notices if i used a high BC 34gr. slug-pellet....but I do think that it would make a differnce at +60 yards.
Something weird doers happen as you approach transonic speeds...every graph/test shows a freakish jump in drag as you move into the Mach ! area (yet not at higher levels). I'll leave it to the engineers to explain why...just enough to know that the "sonic wall" of 1000-1200 fps does absolutely "stupid stuff" to windage.
If you get just barely above transonic at launch...you have to go back though that area down range as velocity declines back to transonic down range....you get a double-dose.
So for lead bullet/slug shooters (rim fire/ center fire/ air gun) it turns out that the best choice is to EITHER keep the speed transonic all the way to the target...or keep it sub-sonic all the way to the target.
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My upcoming articles in HAM will deal with this topic.... but here is a summary.... The drag of ALL projectiles has a huge increase in the Transonic range (Mach 0.8-1.2)…. Here are some typical drag curves....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Drag%20Coefficients%20Including%20ChairGun_zpskfyhpxvr.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Drag%20Coefficients%20Including%20ChairGun_zpskfyhpxvr.jpg.html)
The faster a projectile slows down, the more it drifts in a crosswind.... It is the "lag time" (difference between real world and in a vacuum) that matters, not the "time of flight".... Therefore, regardless of whether it is a pellet or slug, it will drift a LOT more at Mach 1.2 than at Mach 0.8.... This causes the minimum drift to occur at around 850-950 fps muzzle velocity, the exact value dependent on the range to target and the BC.... Here is what happens for a typical pellet at 50 yards....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Wind%20Drift%20JSB%2050_zpsio6vbeef.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Wind%20Drift%20JSB%2050_zpsio6vbeef.jpg.html)
and here is what happens for various slugs at 200 yards....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Wind%20Drift%20G1_zpsix0tzr8y.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Wind%20Drift%20G1_zpsix0tzr8y.jpg.html)
If you look at the curve for a BC = 0.10 (the blue line), you will notice that the drift over 200 yards in this wind strength of 10 mph is 20" at a MV of 900 fps.... That increases to nearly 30" at 1600 fps, and does not fall back to 20" until the MV is about 2700 fps.... :o
Ribbon's observation about the BC being lower at close range is due to the pellet slowing quicker because it is travelling faster.... and a mismatch between the actual drag of the pellet and the drag model used to calculate the BC....
Bob
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My upcoming articles in HAM will deal with this topic.... but here is a summary.... The drag of ALL projectiles has a huge increase in the Transonic range (Mach 0.8-1.2)…. Here are some typical drag curves....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Drag%20Coefficients%20Including%20ChairGun_zpskfyhpxvr.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Drag%20Coefficients%20Including%20ChairGun_zpskfyhpxvr.jpg.html)
The faster a projectile slows down, the more it drifts in a crosswind.... It is the "lag time" (difference between real world and in a vacuum) that matters, not the "time of flight".... Therefore, regardless of whether it is a pellet or slug, it will drift a LOT more at Mach 1.2 than at Mach 0.8.... This causes the minimum drift to occur at around 850-950 fps muzzle velocity, the exact value dependent on the range to target and the BC.... Here is what happens for a typical pellet at 50 yards....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Wind%20Drift%20JSB%2050_zpsio6vbeef.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Wind%20Drift%20JSB%2050_zpsio6vbeef.jpg.html)
and here is what happens for various slugs at 200 yards....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Wind%20Drift%20G1_zpsix0tzr8y.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Wind%20Drift%20G1_zpsix0tzr8y.jpg.html)
If you look at the curve for a BC = 0.10 (the blue line), you will notice that the drift over 200 yards in this wind strength is 20" at a MV of 900 fps.... That increases to nearly 30" at 1600 fps, and does not fall back to 20" until the MV is about 2700 fps.... :o
Ribbon's observation about the BC being lower at close range is due to the pellet slowing quicker because it is travelling faster.... and a mismatch between the actual drag of the pellet and the drag model used to calculate the BC....
Bob
I look forward to the upcoming series.
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So I am going to go ou on a limb here and say I had a good question lol
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I did this last night a comparison with both traveling at 900fps.
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The tests at HAM were done with the same gun with no tuning changes, so the slug had a much lower velocity (860 vs. 940).... I used the numbers for both in ChairGun and came up with the following charts.... Green is for the 16 gr. pellet and blue for the 22 gr. slug.... As you can see, the pellet actually has less drop out to 100 yards, where they are the same POI.... Chart was generated using the same barrel angle, so zero distance was not a factor....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/FX%20Trajectory_zpswbwam7ms.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/FX%20Trajectory_zpswbwam7ms.jpg.html)
Windage is a different story.... The slug has half the wind drift at virtually every distance....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/FX%20Windage_zpshdvyrqqp.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/FX%20Windage_zpshdvyrqqp.jpg.html)
The article at HAM covered the velocity and energy differences, so no point in duplicating that here....
Bob
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As you can see, the pellet actually has less drop out to 100 yards, where they are the same POI....
Interesting. I was expecting the pellet to drop more, especially at that distance
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If you look at the curve for a BC = 0.10 (the blue line), you will notice that the drift over 200 yards in this wind strength is 20" at a MV of 900 fps.
Bob,
I don't know if there is a standard assumed cross-wind for such calculations, but could you share the wind speed you used with us please?
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Sorry, I was being lazy.... I went back and checked, and I did that chart using a 10 mph crosswind....
Bob
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Thanks Bob.
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author=rsterne
My upcoming articles in HAM will deal with this topic.... but here is a summary.... The drag of ALL projectiles has a huge increase in the Transonic range (Mach 0.8-1.2)….
Bob
Great info and another advantage for slugs.
As velocity gets closer to the speed of sound the projectile's "braking" increases.
Less aerodynamic designs are effected more at lower sub-mach percentages. A diablo might have the same braking effect at Mach .7 as a slug has at Mach .8.
Therefore, even though a lighter diablo leaves the barrel faster, 10 feet from the barrel it might already give up that speed advantage.
Slugs aren't just better for long distances. They also shoot flatter and retain more energy at closer distances as velocities increase above 6-700 fps.
Their disadvantage can also be an advantage as diablo's high drag makes them travel less and their lower terminal velocity makes them carry much less energy at further distance.
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Which are limits of length of slugs + FF in your point of view for 3000PSI/24”barrel ?
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That pressure and barrel length limits you to an SD of about 0.17 if you hope to see 900 fps.... That in turn limits the BC.... Smaller calibers can have a higher FF for a given SD.... but all calibers are limited to slugs about 4 calibers long.... and the twist rate depends on the length (in calibers)….
Bob
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I just received the detailed LabRadar data from HAM on the FX Slug and Pellet testing.... This included the local atmospheric conditions at the time of the test, which was 35*F (a cold day), 50% Humidity, 244 ft. above sea level, and 29.5 in.Hg local barometric pressure.... This allowed me to input the actual test conditions into ChairGun so that the results are properly corrected to ICAO conditions.... The G1 model was used for the slugs and the GA model for the pellets....
They shot 10 pellets and 10 slugs, washed but unsorted, and recorded the LabRadar velocities every 10 yards from the muzzle to 50 yards.... I calculated the BC using the average velocities at the muzzle, and both 40 and 50 yards, and also calculated the BC for EACH shot at both distances, and then averaged the BCs, to see if there were any significant differences.... Although there were significant differences from shot to shot in the calculated BCs, there was no significant difference in the resulting average BC using the two methods....
One thing that stood out was that in the slug testing, two shots were outside the typical variation at 50 yards.... one had a high BC and the other low, compared to the same two shots at 40 yards.... At 40 yards the spread in calculated BC for the ten slugs was 10%, while at 50 yards, with those two shots included it was 35%.... Interestingly, the average BC only changed by 1% with them deleted, but they were such a statistical oddity I decided that was the best approach....
Once those two pieces of 50 yd. data were removed, the difference between simply averaging the velocities or calculating the BCs and then averaging those was well into the 4th decimal point.... Regardless, I decided that the best way to calculate the BC for both the slugs and pellets was to average all four numbers, the two 40 yard BC averages and the two 50 yard BC averages, and report that number.... Here are my results....
16 gr. FX Pellet, with MV = 942 fps.... BC (GA) = 0.035
22 gr. FX Hybrid Slug, with MV = 860 fps.... BC (G1) = 0.071
The variation between the highest and lowest of the four BCs used to calculate the above was 2.7% for the slugs and 3.5% for the pellets.... That means that the numbers above should have a total range of error of about 0.001 for the pellet and 0.002 for the slug.... Therefore the BC (G1) for the FX slug in this test, conducted at a MV of 860 fps, is 0.070-0.072....
Bob
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Thanks for the update, Bob.
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So just checking my understanding here
The BC on box is too high as is the pellet trajectory on box and the slug trajectory is too flat on box
Is that all true?
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Bob,
Interesting results - thanks for that analysis. Interesting that the variability in BC was higher on the pellets than the slugs - that is precisely what I think one would expect, given the low BC to start with, and sensitivity to the Form Factor . . .
I have done some testing for BC on my pellets as shot, but have always worked with averages as I only have one chronograph to use at two distances. In every case, I have always seen much higher variation in speed downrange than at the muzzle, and the only thing that I can think of to explain it would be variability in BC (especially given that the variation at the muzzle was pretty tight, on purpose). I think it is an under explored factor on achieving the best accuracy possible at a distance (and in my mind, part of why head size is typically so important to accuracy, given the impact of the "smeared" lead area on the head). Thanks again.
JB - the illustration on the box really had no data at all, and the illustration was just that - an illustration . . . no real world comparison provided.
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Alan, in much of the testing I have done, I actually found LESS variation in velocity downrange than at the muzzle, with some obvious outliers which are likely damaged pellets.... I think what is happening is that the weight variation favours a higher BC for the heavier pellet, which should start out a bit slower at the muzzle.... and the result is that they even out somewhat downrange.... Weight variance actually has little to do with vertical stringing, there have been several threads dealing with that....
The diagram on the box should be taken with a grain of salt.... it is advertising, nothing more.... The BC claim of 0.080 could well be true at SOME velocity, under some other conditions.... Overall, it is within 12%, so not that far afield, IMO.... The trajectory difference between 0.071 and 0.080 is negligible, and the wind drift would be proportional to the BC.... If you shoot in other conditions (hotter, higher altitude, etc.etc.) you could easily have an EFFFECTIVE BC different by more than that....
Bob
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Hopefully some helpful info: The BC listed on the Hybrid box was determined after extensive testing at velocities higher than what HAM just shared. We have found that higher velocities absolutely affect the BC (I'm sure Bob can confirm). Our recommended sweet spot to shoot the Hybrids is 940-950fps. As Bob has explained properly other factors do play into calculating BC and it's impossible to list on a box the actual BC of what you'll get out of your rifle. Our goal of listing the G1 BC was to give everyone a rough starting point for their testing. We've had guys shooting them above 1,000fps with great accuracy and even higher BC than 0.80, and some shooting more in the 840fps range with lower BCs but still good results (much like HAM showed). Instead of just listing best case scenario, we felt 0.80 was a good healthy average many should be able to obtain.
We realize that many distrust the Pro Shooters / YouTubers we work with, so we'd say go pick up a box, run tests in your guns, and share the results. We made sure they'd be readily available when we released them to the market so everyone wouldn't have to pontificate of what they could or couldn't do, but simply go find out for yourself. We think you'll be pleasantly surprised.
Thankful for everyone's constructive talk. Our goal is just to keep moving forward our sport and push the boundaries of what airguns can do.
- Jonathan
PS - Hope you guys understand why our last post about Hybrids before the actual release date was holding back some info. We wanted to release news about a product and have anyone who was interested be able to act right away to pick them up. Something we hope can happen more and more in our sport instead of months of waiting. Thanks again everyone.
Alan, in much of the testing I have done, I actually found LESS variation in velocity downrange than at the muzzle, with some obvious outliers which are likely damaged pellets.... I think what is happening is that the weight variation favours a higher BC for the heavier pellet, which should start out a bit slower at the muzzle.... and the result is that they even out somewhat downrange.... Weight variance actually has little to do with vertical stringing, there have been several threads dealing with that....
The diagram on the box should be taken with a grain of salt.... it is advertising, nothing more.... The BC claim of 0.080 could well be true at SOME velocity, under some other conditions.... Overall, it is within 12%, so not that far afield, IMO.... The trajectory difference between 0.071 and 0.080 is negligible, and the wind drift would be proportional to the BC.... If you shoot in other conditions (hotter, higher altitude, etc.etc.) you could easily have an EFFFECTIVE BC different by more than that....
Bob
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Great info, Bob
Obliquely related to this, is a thought that occurred to me, shooting my new P-Rod:
The P-Rod gets only 19 shots from 2800 to 1800 PSI at a 4% ES, due to its tiny air reservoir. While evening out velocity is great, and what regulators are supposed to do, the thought occurred to me, that if you shot an unregulated PCP from 3000 to 1000 PSI, the degree of pellet skirt flaring (or ballooning, if you like) would be more at the higher pressure, and diminish though the shot string. As such, even if a clever valve could achieve a low velocity spread, 2 feet from the muzzle, the difference in skirt shape over that applied starting pressure range, could change the shape of the pellets; and thereby their drag and BC.
My thinking is that higher pressures would flare pellets skirts more, and come closer to converting a diabolo pellets into a more cylindrical slug. Certainly, pellets shot out of pumpers at very few pumps show an almost out of the can diabolo shape. This can be seen to change when shooting the same can of pellets at a higher number of pumps. The most obvious thing is the length of the bore diameter "land" created at the rear of the skirt, for a given actual bore (choke) diameter. When the skirt engagement is longer due to higher firing pressure, the skirt is blown into a more rounded shape, than the original straight cone shape.
Now, to make the above relevant to your HAM BC testing; was this data collected with the PCP tethered to a large air tank; or was the reservoir pressure allowed to decay over the 20 shot test? If the PCP's built-in tank was large, then my point is probably moot. I am certainly thinking about actual peak firing pressure in the most general sense, as a BC modifier that show at longer ranges...
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Jonathan, thanks for your comments about how the BC of the FX Hybrid slugs changes with velocity.... This is, of course, an indication that the G1 drag profile is not a very good match for the shape of the slug, something we always face with pellets and slugs alike.... Hopefully over time we will end up with better drag models, that better match our projectiles.... That will allow far better calculations for trajectory and wind drift.... After all, a slug launched at 1000 fps travels through the 940-950 fps range you measured the BC = 0.080 at.... and further out, through the 860 to 770 fps range that HAM measured the BC = 0.071 at.... as it travels downrange.... Perhaps eventually FX will supply a complete Cd drag model for their slugs like Lapua do for their bullets.... That would be the ultimate....
Subscriber, you are quite right that pellets skirts change shape depending on the pressure they are launched at.... I'm sure that has an effect on the Cd and hence the BC.... I am not involved in the BC testing done by HAM, but quoting from their website....
all HAM airgun Ballistic Coefficient testing has been undertaken by the same experienced, dedicated testers, using the same FX Impact air rifle, set to full power, with all FPS measurements recorded using the same Labradar Doppler Radar system.
The Impact is a regulated PCP, so all shots should be subject to the same pressure, within the mechanical limits of such a gun....
Bob
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Correct, the G1 profile was the best of the available models but not a perfect fit. Agree that a better drag model for airgun slugs would be very helpful as we grow our sport.
Jonathan, thanks for your comments about how the BC of the FX Hybrid slugs changes with velocity.... This is, of course, an indication that the G1 drag profile is not a very good match for the shape of the slug, something we always face with pellets and slugs alike.... Hopefully over time we will end up with better drag models, that better match our projectiles.... That will allow far better calculations for trajectory and wind drift.... After all, a slug launched at 1000 fps travels through the 940-950 fps range you measured the BC = 0.080 at.... and further out, through the 860 to 770 fps range that HAM measured the BC = 0.071 at.... as it travels downrange.... Perhaps eventually FX will supply a complete Cd drag model for their slugs like Lapua do for their bullets.... That would be the ultimate....
Subscriber, you are quite right that pellets skirts change shape depending on the pressure they are launched at.... I'm sure that has an effect on the Cd and hence the BC.... I am not involved in the BC testing done by HAM, but quoting from their website....
all HAM airgun Ballistic Coefficient testing has been undertaken by the same experienced, dedicated testers, using the same FX Impact air rifle, set to full power, with all FPS measurements recorded using the same Labradar Doppler Radar system.
The Impact is a regulated PCP, so all shots should be subject to the same pressure, within the mechanical limits of such a gun....
Bob
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Jonathan, thanks for your comments about how the BC of the FX Hybrid slugs changes with velocity.... This is, of course, an indication that the G1 drag profile is not a very good match for the shape of the slug, something we always face with pellets and slugs alike.... Hopefully over time we will end up with better drag models, that better match our projectiles....
Bob
Production of a drag model for slugs which will fit over a wide Mach number range will be difficult due to the variations in the size of the large flat areas (meplat) at the front of many of them coupled with the detail shape at the edges of the meplat. Very small amounts of rounding on the edges can have a large effect on the drag coefficient as well as the aerodynamic stability. I produced some drag curves for wadcutter pellets for Chairgun some time ago which showed the difficulty of producing a single reference drag curve for projectiles with large flat front facing areas as the shape of the Cd curves in addition to the Cd values changed as Mach number increased.
Individual drag curves similar to those used in artillery fire control systems is the way to go but their creation could be problematical. Years of experience using tracking radars of all kinds have shown me that using fixed head doppler radars can easily give large errors in Cd values due to improper setup of the trial instrumentation and radar internal software which modifies the output to smooth out the data. We ended up always using a very large tracking doppler radar with a fully tracking head which is obviously out of the question for pellet makers or researchers. Aerodynamic prediction software is available, some of which will work for slugs and bullets, which can give initial values but again the very large meplat values used on many slugs can give gross underestimates of drag as the software was not designed for such blunt shapes.
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I would prefer to see a pellet of similar mass (Baracuda Match 21.14gr) to the FX Hybrid shot at the same velocity, not just the same gun settings.
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Miles, I agree that trying to develop an exact drag model to cover a larger range of projectiles would be next to impossible.... What I was suggesting was the approach used by Lapua, where they have a Cd curve for each bullet.... If FX developed that for each of their slugs, and provided the software to use it (like Lapua does)…. they would have something that nobody else does.... customized ballistics prediction for each slug they make....
The limited playing I have done with LabRadar outputs leads me to believe that instead of using the Doppler velocities (which can flop around like a wet fish)…. a far better approach is to use the time/distance data, plot that, generate the t/d equation, and then use the first derivative for the velocity and the second derivative for the deceleration.... Even so, there is such a difference shot to shot, getting perfect results is a muggs game.... and stitching together several sets of data to cover a large velocity range may well prove impossible.... ::)
When I retire in 2021, I plan to use the LabRadar I was awarded by the AirGunGuild to do some serious work on developing a better drag model (or 3) for pellets.... I think you would agree that the current GA model underestimates the increase in drag in the Transonic, and I think at low velocities as well.... Even if what I come up with isn't perfect, perhaps we can at least have something closer to reality than what we have now.... I have a feeling that the G1 model we use for slugs is not that great either in the Transonic range.... because we typically use slugs with a rather large Meplat, not the Spitzer nose of the G1 drag model....
Anyways, that is my hope.... Perhaps I will be just wasting my time.... ::) …. but I will guarantee you I will learn a lot and have fun doing it.... After all, what more can a Hobby give you than that.... 8)
Thane, I agree I would have liked to seen a comparison to a pellet of similar mass, at similar velocity.... ;)
Bob
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…. but I will guarantee you I will learn a lot and have fun doing it.... After all, what more can a Hobby give you than that.... 8)
Bob, thank you for this reminder! Love it. :-)
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Miles, I agree that trying to develop an exact drag model to cover a larger range of projectiles would be next to impossible.... What I was suggesting was the approach used by Lapua, where they have a Cd curve for each bullet.... If FX developed that for each of their slugs, and provided the software to use it (like Lapua does)…. they would have something that nobody else does.... customized ballistics prediction for each slug they make....
Bob
Bob
That is exactly the approach we used on the artillery fire control and, during the last years of my career, we were using a large multi million dollar radar to track bullets of all sizes from 4.5mm to 14.7mm and derive drag laws for each bullet design from the different types of guns. The Lapua data is the way to go, though I have some doubts about some of their data which seems to go up to Mach 5 for their bullets and does not match very well the drag curves we were producing for some of the bullets. All of the trajectory software I use has always used Cd/Mach number curves, not BCs having been designed for artillery shells.
On the bullet trials we were trying to fill in the very short range data using the raw data from the fixed head muzzle velocity radars (like the LabRadar but more powerful), used to obtain the muzzle velocities, but it was not very successful, often producing unrealistic drag curve shapes. We concluded it was because the radar units were often smoothing the data before printing it out making the drag curve shape a function of the smoothing curve, not the data. I suspect that LabRadar does the same thing as most of the data I have seen is just too smooth to be true raw data. Getting true raw data from the fixed head radars is not always straight forward. We always used a minimum of two muzzle velocity radars for all shots which had to agree with each other to less than 1m/s. Getting matching readings with small arms prooved very difficult, the radars being very sensitive to positioning and aiming with the readings often drifting away from each other during 10 round serials.
On the GA drag law Chairgun also has a version of my drag law produced for AA Field pellets using a mixture of prediction and calibration with measured data. The drag law is here.
Mach Cd
0.1 0.8
0.15 0.73
0.2 0.62
0.32 0.44
0.4 0.334
0.5 0.3103
0.55 0.318
0.6 0.327
0.65 0.332
0.7 0.363
0.75 0.404
0.8 0.455
0.9 0.56
1 0.8
You can see the high and low speed data is higher than GA. If you want to use this drag law with the usual BC value for this pellet you will have to either devide the CD values by the form factor value or use the sectional density as the BC value.
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As the shooter for all of the HAM BC testing, I just want to throw one thing into the slug design - LENGTH. There have been several pellets that have come through that have been too long to fit into airgun magazines. Sure, some bolt action airguns can handle them, but almost all of the airguns produced these days have magazines. Unless the gun manufacturers decide to produce guns with magazines that will handle them, the pellet manufacturers should probably keep the lengths down to something that they can sell.
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Miles, that is a great set of data.... I don't see it in the latest version of ChairGun that I downloaded, but I have added it to my spreadsheet of drag laws, and plotted it along with all the others from ChairGun…. Photobucket is down right now, but as soon as it is back up, I will add that chart to this thread.... It is VERY different from all the others, particularly under 500 fps.... I wonder why our Diabolo pellets have such high drag at low speeds?....
Bob
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As this is about FX slugs, I would like to suggest FX equip their shooting tunnel with multiple light screens, at 5 meter increments, to the end of their on site 40 m range. The ones nearest the muzzle could be spaced at 0.5 m to capture "muzzle velocity". So 8 or 9 screens, including the "muzzle" pair.
Yes, LabRadar is just so convenient; especially to cart out to various indoor or outdoor ranges. However, for a fixed lab setting or factory, capturing the actual beam breaking time for each pellet at a number of discreet fixed ranges would seem to provide very good raw data for BC measurement. If the screen spacing were close enough, it would also show if any projectile had marginal stability, because yawing projectiles have more drag, when they travel more obliquely through the air.
Obviously, setting up such light screens in a shooting tunnel to 100 meters, at 1 meter intervals would be preferred. However, that would cost a lot more to install than a LabRadar unit; and for some, would seem like a step backwards in technology. I don't care about backwards. I prefer accurate information that has not been "smoothed", to cover up shortcomings of a particular system.
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EDIT: Deleted. I read CD as BC...
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I agree, for a fixed, laboratory setup, a 100 metre tunnel with screens every metre, would be the ideal setup.... It isn't a "backwards" step if it supplies higher quality data.... Besides, it should show up things like a drag increase due to wobbling or spiraling, and what distance it started at....
Another thing I would like to see is an "easy to use" spreadsheet or calculator that would allow you to input Cd values such as Miles listed above, plus the caliber and weight of the projectile, the muzzle velocity and the wind parameters.... and output the trajectory and wind drift.... Let's forget about using BC's, which are comparing the Cd to some drag model that won't match up.... and use the raw Cd data instead....
Bob
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I would like to see is an "easy to use" spreadsheet or calculator that would allow you to input Cd values such as Miles listed above, plus the caliber and weight of the projectile, the muzzle velocity and the wind parameters.... and output the trajectory and wind drift....
Bob
Yupp, I agree.
And whenever I get my second chrono back from the US (I "shot" it with too much voltage 😟) — I want to begin getting data for my preferred gun-pellet combinations.
Because the spreadsheet or program you're asking thankfully exists. 😊
Strelok Pro.
Here're a couple of screen shots (just to see, no valid data).
Matthias
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Matthias.... I didn't realize you could put a custom drag model into Strelok Pro.... Is there a limit to the number of steps (data points) you can input?....
Bob
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Bob,
I counted over 200 data fields....!
As this app needs to work for people shooting bullets traversing several mach on their way from the muzzle to target a mile or two out, it seems appropriate to have a bunch of data fields...! 😄
Matthias
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Miles, it was great to hear from you the other day.... I plotted your drag model for airgun pellets and added it to a chart I had of other drag models from ChairGun…. The red line below is the raw data as stated by Miles above....
(https://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Drag%20Coefficients%20including%20Miles_zpshf87luhi.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Drag%20Coefficients%20including%20Miles_zpshf87luhi.jpg.html)
Miles informed me that his drag model is also available in ChairGun, in the list of Custom Drag Profiles.... You can access it by going the the "Toolbox" Tab, clicking on that and then scrolling down the dropdown menu to "Custom Profile Tools" and then selecting and clicking on "Select Custom Profile".... From the available files, select "MilesMorrisProfile.pro" and click on that.... That will load his drag profile into the "GU" drag function in ChairGun, and you can use it like any of the other drag profiles.... Note that the authours of ChairGun have "adjusted" it to track along with the values of the "GA" profile, so that BC calculations made using it "make sense" instead of being much higher for a given SD.... I suspect that they made a similar "adjustment" to the GA profile so that it produces BCs similar to the G1 profile previously used for pellets....
This information has little to do with the thread on FX slugs.... but I wanted to include it in this thread because that is where Miles (ballisticboy) first published it on the GTA.... He has worked in external ballistics of projectiles for the last 40 years, by the way.... 8)
Bob
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As the shooter for all of the HAM BC testing, I just want to throw one thing into the slug design - LENGTH. There have been several pellets that have come through that have been too long to fit into airgun magazines. Sure, some bolt action airguns can handle them, but almost all of the airguns produced these days have magazines. Unless the gun manufacturers decide to produce guns with magazines that will handle them, the pellet manufacturers should probably keep the lengths down to something that they can sell.
That is a very important limitation indeed. If they don't fit the magazine people won't shoot them. It seems that 10-11mm is the length limit for mags. In practice that means that for a good BC we should go down in caliber to allow longer bullets. Unfortunately .177 twistrates are too slow for that in general leaving .172 as a working solution.