.25 cal. Ballistics Coefficients

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Offline rsterne

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.25 cal. Ballistics Coefficients
« on: April 18, 2012, 08:16:26 PM »
I spent the day measuring the Ballistics Coefficients of all the .25 cal. pellets I have.... I used my Hayabusa, set up for about 960 fps with JSB Kings.... I shot 5 shots groups inside with the Chrony at 1 yard from the muzzle.... I made sure the tank pressure stayed between 2000-3000 psi for all strings, which is 100 psi above the regulator setpoint of 1900.... I then repeated all the strings outside with the Chrony at 25 yards from the muzzle.... and I even shot all the strings at the same part of the tank fill as I did the first time to be as consistent as possible.... The BCs were then calculated using ChairGunPro.... Here are the results.... Remember that these BCs are only valid for this particular rifle at the velocities specified.... although they should be a good indicator of what to expect....



Here are a few comments.... The JSB Kings had the highest remaining Velocity at 25 yards, and the tightest Standard Deviation at that distance.... I was a bit disappointed in the BC of only 0.024, but then I thought about how fast they are being driven, and it's very possible (in fact probable) they are beyond the sweet spot of the BC curve at 960 fps.... The H&N Baracudas (aka Beeman Kodiaks) had the highest BC at this power level.... The maximum Energy went to the EunJin Pointed pellets, both at the muzzle and at 25 yards.... but of course they had the lowest velocity as well....

As far as I'm concerned, a .25 cal is all about power and range.... Based on that, I'm only going to test those pellets which had over the 36.2 average FPE remaining at 25 yards for accuracy.... That means only those eight pellets with a BC of over 0.018.... Those that show promising accuracy will then get more work to determine the velocity where the BC peaks.... I'll keep you posted on further testing.... 

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline Lambchops

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Re: .25 cal. Ballistics Coefficients
« Reply #1 on: April 18, 2012, 08:48:36 PM »
Superb info Bob. One question though, what is a Ballistic Coefficient and why is higher better?
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Offline yoshi800

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Re: .25 cal. Ballistics Coefficients
« Reply #2 on: April 18, 2012, 08:54:50 PM »
Wow, what a lot of work!  Thanks for the info!  Don't BC's change with the air density also?
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Offline JTank70

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Re: .25 cal. Ballistics Coefficients
« Reply #3 on: April 18, 2012, 09:28:38 PM »
This is Good.  There is a lack of Ballistic info on .25 caliber.

I am anxious to see your further testing results on the top eight.

Thanks for all the work you are doing on this Bob.
JT
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Offline rsterne

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Re: .25 cal. Ballistics Coefficients
« Reply #4 on: April 18, 2012, 10:16:35 PM »
The Ballistics Coefficient is a measure of how the pellet retains velocity.... the higher the number the more velocity it retains.... so bigger is better.... Round nosed pellets are king, wadcutters suck.... pointeds and hollow points are in between.... Heavy pellets generally are better than light ones.... The BC tends to fall off at high velocities as well....

I'm not sure if the BC changes with air density, but how it affects the velocity would....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline airpuffhunter

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Re: .25 cal. Ballistics Coefficients
« Reply #5 on: April 18, 2012, 11:31:38 PM »
very interesting
thank you

Offline Lambchops

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Re: .25 cal. Ballistics Coefficients
« Reply #6 on: April 19, 2012, 12:23:51 AM »
The Ballistics Coefficient is a measure of how the pellet retains velocity.... the higher the number the more velocity it retains.... so bigger is better.... Round nosed pellets are king, wadcutters suck.... pointeds and hollow points are in between.... Heavy pellets generally are better than light ones.... The BC tends to fall off at high velocities as well....

I'm not sure if the BC changes with air density, but how it affects the velocity would....

Bob

Thank you Bob, you explained it very well.
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Offline GunnerAl

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Re: .25 cal. Ballistics Coefficients
« Reply #7 on: April 19, 2012, 02:47:40 AM »
I shot 5 shots groups inside with the Chrony at 1 yard from the muzzle.... I then repeated all the strings outside with the Chrony at 25 yards from the muzzle

This is the only part of this fantastic experiment that I have a problem with... To shoot the first half of an experiment at one venue then the other half at a completely different venue...

Now, I am NO expert with the chrony nor with calculating BC's but I would have thought it would have been better to have had one chrony at 1yd and the other at 25yds already set in place in which to measure EACH shot at one time to get the EXACT one off flight path at the moment... I know what I am saying sounds like a tall order and not many of us have two chronys but I think this is the ONLY way to do this and hope to ever get any half accurate relationship between near and far shot flight paths from an individual shot... Let's say that by some freak of nature, all the shots you measured indoors read slightly above what actually took place,, then outdoors they all read slightly below... This would then affect the outcome of your results by a wide margin and your attained BC's may well be all too low, or of it all hppened the other way around the BC's might all be too high,, or it could have been a mixed bag,, some high, some low... While you took extreme care to monitor the pressures in your test rifle, you may have inadvertently overlooked the two part test (part 1 at 1yd and part 2 at 25yds) which created a measurable margin of error...

Let's try to look at it a little closer and a little more extreme to exaggerate the possible margin of error... Let's say you have a rifle that shoots a high of 955fps and a low of 920fps over a given amount of shots at 1 yd... Let's say you shot your first pellet at 1yd and it resulted at 920fps then you set up and fired it at 25yds to get your second reading, which turned out at say 885fps... Then you decided to repeat it. First shot at 1yd 955fps this time and the second shot at 25yds again 885fps. How do you judge the average? As far as close/far realationships go, are you getting high(@1yd) and high(@25yds),, high(@1yd) and low(@25yds),, low (@1yd) and low(@25yds),, low (@1yd) and high (@25yds)... Can you see what I'm driving at here...???

If you had one chrony in place at 1yd and another in place at 25yds at the same time and you took both readings per shot from both chronys, then there is no doubting your results as they are directly related - near and far reading,, because both readings came from the one shot... Shooting a handful at 1yd then a handful at 25yds and trying to inter-relate them is kind of hit an miss, a shake of the dice, a best guess and lots of room for error...

I am simply looking at this in a scientific way, in that your tests, although mighty and enlightening, may well be flawed, however it was a mammoth task... Please don't take what I have said as a personal attack or anything like that,, it's just that I have been playing this ballistics game for so many years that I have seen and experienced so many miscalculated data's that this immediately hit me right between the eyes when I read it... It was well done and presented though...!!!

I'm not saying I know the answers,, just that I thought I'd point out one "possible" region of error...
« Last Edit: April 19, 2012, 02:56:27 AM by GunnerAl »

Offline huklbery

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Re: .25 cal. Ballistics Coefficients
« Reply #8 on: April 19, 2012, 09:36:22 AM »
Wouldn't the sample size help to "moderate" the error?  There are many variables to give the pellet flight but the sample size should help there.

Mark
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Offline dukemeister

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Re: .25 cal. Ballistics Coefficients
« Reply #9 on: April 19, 2012, 10:59:35 AM »
.....t I thought I'd point out one "possible" region of error...
I believe the value of the experiments is to a) show which pellets are likely to perform (i.e., group) well and carry retained energy to a target at a distance and b) give an estimate of BC for us to use in software like ChairGun. The results are "estimates" at best and as acknowledged by Bob pertain to his Hayabusa rifle under the conditions he tested. Probably the reason there is no BC printed on any pellet tin is that BC is a variable, the actual value varies in both time and space for every pellet fired.
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Offline WHITEFANG

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Re: .25 cal. Ballistics Coefficients
« Reply #10 on: April 19, 2012, 12:12:21 PM »
Great to see the interest in the .25 cal. Not many of use have any ideal of what they can and will do. For me the .25 has my interest for my shooting area. Been shooting my power house guns allot lately and need to go back to a comfortable zone.
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Offline rsterne

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Re: .25 cal. Ballistics Coefficients
« Reply #11 on: April 19, 2012, 01:42:05 PM »
GunnerAl.... You are absolutely correct, the ONLY way to measure the BC accurately on any individual shot is to use two Chronys, one at 1 yd., the other at 25 yards, and calibrate both to make sure that the angle the shot is going through the Chronys on, and the placement relative to the sensors, is taken into account and consistent.... Then you could average the BCs of (say) 5 shots to come up with an average BC under those precise conditions....

Now let's look at what I actually did.... First of all, I used a rifle that has a maximum known velocity spread with JSB Kings over the tank pressures used of only about 1% (ie 9 fps).... Further, that velocity varies in a relatively predictable way during the drop from 3000 psi to 2000 psi, and I used the same portion of the tank fill for any given pellet, further reducing the velocity variation due to the gun itself.... Secondly, I took a 5 shot string, recording the AVERAGE velocity, and the SD.... I did the same thing at 25 yards.... If you want an indication of the potential accuracy of the experiment, then add the two SDs for the two distances, and divide that by the average velocity at those two distances.... In the case of the JSB Kings, that is 4.6 / 908 fps = 0.5%.... In the case of the Lasers, that is 19.8 / 893 = 2.2%.... You will note that I only specified the BC to three decimal places (ie two significant figures, even though Chairgun calculates them to four, ie 3 significant figures).... Since 2.2% of the highest BC (0.039) is 0.0009 (which is likely the worst case) I feel quoting the BCs to three decimals (two significant figures) to reasonably represent the accuracy of the test.... Statistically, the BC should be the most accurate for the pellets having the lowest SDs....

It is true that there COULD be a difference between indoors and outdoors.... However, I used the indoor lighting kit on the outside shots, and covered the Chrony with a cardboard shade to exclude as much stray light as possible.... When you consider that virtually every time you find a BC published for a pellet it is a different value.... plus I gave the disclaimer that these numbers are only valid for my Hayabusa at the velocities specified.... I feel comfortable in using them.... If you feel that there are too many possibilities for error that you cannot trust them, I have no problem with that.... You will note that the default tolerance used in Chairgun (for quality pellets) for the BC is 10% (for example, a BC of 0.020 could be 0.018 to 0.022).... If you activate the tolerance graphing capability, you will find the upper and lower trajectories corrected for that, including (again at default) a 1% tolerance in muzzle velocity (eg. 900 fps could be 891 to 909)....   

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline SAADE

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Re: .25 cal. Ballistics Coefficients
« Reply #12 on: April 19, 2012, 03:59:33 PM »
Dukemeister: Yes, and, with all else constant, a change in altitude usually has the most effect on ballistic coefficient, followed by temperature and then humidity. These are not absolutes because those three characteristics of our weather or atmosphere are inter-related. Most published info on powder burner B.C.s is based on sea-level or 29.6-ish barometric pressure. Other than extreme changes in altitude, the smaller bore airgun pellets are more bothered by (even) light winds and rain than atmosphere changes (e.g. density, temp etc).
Brian in Idaho

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Offline rsterne

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Re: .25 cal. Ballistics Coefficients
« Reply #13 on: April 19, 2012, 04:05:56 PM »
I continued with the testing today.... What I did was back the power of the gun down so that the muzzle velocities were close to the 25 yard velocities in the first set of tests.... I am trying to approximate what happens between 25 and 50 yards.... The RWS Hollow Points were dropped as they were not very accurate so would be hopeless at 50 yards.... I ran out of the EunJin Pointed, so had to leave those out as well.... The testing followed the exact same procedure as yesterday, with the following results....



I am concentrating my efforts on the JSB Kings as they are obviously the most accurate out of this gun.... The plan is to continue backing down the power so that each chart moves out about 25 yards for those pellets.... There will be some gaps for other pellets, but the data should be continuous enough to show the trends for the BCs.... More to follow....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline WHITEFANG

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Re: .25 cal. Ballistics Coefficients
« Reply #14 on: April 19, 2012, 04:21:08 PM »
Good point. Smaller cal suffer more even on PBs. Even those that are blistering the fps speeds. Again, elements of temp, etc. Always remember in metal properties: Heat expands and cold contracts. Clearences change due this as well. Then throw all your other controlled or not environments. Point being no  1 gun is going to give you a true expectation to your setting. What we share with each other on findings is only a base calculation at the time of test. Just like code inspection: NDT inspection from a CWI is only good for that time of inspection.
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RWS 460 .22 .135 VORTEK/FANG
RWS 460 .20 LW JM/FANG
RWS 48 .20 135 VORTEK/FANG LW
RWS 52 .25 .135 VORTEK/FANG 2002
RWS 52 .25 135 VORTEK/FANG #3 OF 24
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Offline GunnerAl

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Re: .25 cal. Ballistics Coefficients
« Reply #15 on: April 19, 2012, 06:09:27 PM »
At the end of the day, I have to say you did a darn good job. I certainly would like to do similar but I guess like the hoards, I just have to accept the manufacturers BC figures about their products. I can however, work out my own velocity charts, as the manufacturers velocity claims are what really get under my skin. I just can't figure out why they seldom give the energy that thier guns give, as opposed to distorted velocities. I say "distorted" becuase some of them can actually be achieved, but most of us would never use ammo light enough to reach them,, because it may cause damage to the gun and/or pellets of these light weights serve little or no purpose for most of our practical daily use of our airguns. I mean, who uses .177 pellets of less than 7 gr or thereabouts for hunting with an airgun..?? Having a chrony and actually chronying each of your guns and each different pellet will give a truer indication of your guns potential, but only as a guide, not as the undisputed truth because just like you in trying to conduct your own tests, there are too many one-off's and misleading values that aren't revealed to us from the manufacturers, to even contemplate conducting an accurate test.

Anyway, your results help me to confirm that all you read about pellets on many sites may not be the asbolute truth and that tests may reveal more knowledge... I'll follow your tests and results as it is above all else - interesting..!!!

Offline rsterne

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Re: .25 cal. Ballistics Coefficients
« Reply #16 on: April 19, 2012, 06:58:20 PM »
Third set of data.... approximating BCs from 50-75 yards in my Hayabusa....



The RWS SuperDome isn't accurate enough to continue further testing in this gun.... More to come....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline EKIM

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Re: .25 cal. Ballistics Coefficients
« Reply #17 on: April 19, 2012, 08:48:02 PM »
Wow that is some work you put in there Bob! Excellent findings and testing! I find this especially useful since there are a lot of people interested in .25 myself included. These results would be a great addition to the GTA library or stuck to the the top here. 
---MIKE---

Offline rsterne

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Re: .25 cal. Ballistics Coefficients
« Reply #18 on: April 21, 2012, 09:01:45 PM »
Here are the last two set of data.... The first approximates the BCs between 75-100 yards....



The second set of data approximates the BCs between 100-125 yards....



This is nearly the lowest power level I can achieve on my Hayabusa by simply adjusting the transfer port restriction.... It should be noted that the BC of the JSK Kings peaked at a velocity of about 700 fps, which is just about what I expected.... They are, after all, the lightest pellet in the test series.... All five of these pellets produced about dime sized groups shooting through the Chrony at 25 yards, and I wasn't exactly being very careful.... They all need to be assessed for accuracy at longer ranges in the summer when I have the opportunity.... Now to analyze the data to see how the BC varies with velocity....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

Offline rsterne

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Re: .25 cal. Ballistics Coefficients
« Reply #19 on: April 21, 2012, 10:48:01 PM »
After compiling the raw data, I graphed the Ballistics Coefficient vs Velocity for the best pellets.... I did one extra data point for the H&N Baracudas with the gun set for maximum power, with the data collected over just 10 yards, to see if the BC rolled over at about 900 fps, and in fact it did, dropping from 0.039 down to 0.033.... Here is a plot of that data, including that additional data point....



I didn't have enough EunJin Pointed pellets to test at various velocities, so the only data point taken is shown.... You will see that several of the lines are "wavy", and perhaps the tendline should be smoothed (or maybe not).... I'll let you draw your own conclusions.... The JSB Kings did, in fact, exhibit the typical curve I have grown to expect of them, peaking at about 700 fps.... What that means, is that once they lose the initial 100 fps or so (in the first 25 yards), the BC is above 0.030, and continues to increase out to about 100 yards.... It probably isn't a good idea to push them much beyond 900 fps.... they are, after all, the lightest pellet in the group.... In my Hayabusa, they were noticably more accurate than any of the other pellets, at all the velocities tested.... and had the flattest trajectory....

Using the above graph, and using Chairgun, I then compiled a table showing as closely as possible what I could expect when shooting the various pellets out of my Hayabusa when set for ~53 FPE (the way I started the testing).... I used the muzzle velocities for each pellet recorded at that power setting, and then using Chairgun I calculated the velocity every 25 yards.... I used the BCs from the graph above for each calculation.... Here are the results....



The "Avg. BC/100" numbers are determined using ChairGun.... I input the muzzle velocity, and then changed the BC until I got a number that matched the 100 yard velocity in the table.... It represents a number you could use to determine the trajectory, velocity and energy at 100 yards without going through all the steps.... The ACTUAL trajectory would vary slightly from what ChairGun would predict using those numbers.... as an example, for the JSB Kings, the trajectory would be a bit more curved initially, and then actually flatter as you go out further (relative to ChairGun)....

You can see that from about 10 yards out, the H&N Baracudas have the most FPE.... They also have the highest average BC, and although the BC does start to drop off at velocities over 850 fps, they would be an excellent choice for any gun that can shoot them fast and accurately.... The EunJin Domes have good close in power, but their relatively low velocity and mediocre BC make them a poor choice at long range.... both for trajectory and wind drift.... It would appear that driving them over 700 fps costs significantly in terms of the BC, as you might expect with a relatively blunt pellet.... The Predator Polymags likewise have a drop in BC which hurts their performance over about 750 fps.... They were close behind the JSB Kings in terms of accuracy.... but their retained energy at 100 yards was under 20 FPE.... and the lower BC will make them sensitive to crosswinds.... The RWS SuperDomes simply weren't accurate enough in my Hayabusa to bother with.... In fact, it wasn't unusual to have to shoot 10 (or more) shots at 25 yards to get 5 that didn't produce an error or no velocity reading.... They did have a very good BC, however, so if your gun shoots them well they bear investigating.... The Benjamin Domes had a consistently high BC, significantly better than the JSB Kings at the higher velocities.... I didn't drive them fast enough to see the fall-off in the BC, but I'm betting it will start to drop at over 900 fps....

So after all this testing, I have four pellets on my short list.... The most accurate and flattest shooting were the JSB Kings, but in terms of ballistics the Benjamin Domes are very close, I'll have to see how the accuracy compares at long ranges.... I'd love to use the H&N Baracudas if they prove to be accurate enough, they certainly have the power.... The Predator Polymags are teasingly accurate, it will remain to be seen if that is enough to overcome the lack of energy and susceptability to wind drift at longer ranges....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine (Grouse Gun), 2260 PCP Rifle (37 FPE), 2560 PCP Rifle (52 FPE), .22 BAM B-26, .22 BAM B-51, Hatsan AT-4410 Long (70 FPE),
"Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357 unregulated; working on the Mk.III, a .410 shotgun, and .458 cal)

How do you word it... "Air Guns" or "AirGuns"?