Strelok, Chairgun & Other programs and Ballistic Coefficients....

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For the most part, I agree. But is isn't just airguns, as the same series of improvements have been seen in powder guns too. I think the key words here are, manufacturing consistency. Unfortunately, I think pellet consistency isn't as good as it could be. It is not uncommon for a tin of 10.5 grain pellets to vary by as much as a 1/10 of a grain. Most decent 6 mm, 95 grain match bullets won't vary that much, but of course they cost many times more. Obviously, this level of variance makes long-range velocity/BC calculations nearly worthless. 


And I agree with the advertising hype issue too. For example, Crosman says their 397 will develop 14.9 FPE. That would require 800 FPS using a 10.5 grain pellet if I did the math correctly. No darn way is this possible. When I ask about that, they never answered my emails. 
 
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Wow AZ. Firstly a big THANK YOU for taking the time to write this out for us. + 10 accuracy to you mate.

I found this to be very educational and now I can explain why my pellets sometimes land half a mil dot up or down at 150 yards when the weather changes. This is super useful especially for someone like me who relies heavily on Sterlok. Please help me understand how to calculate the BC at different distances. I shoot at anything between 50 to a 150 yards. I am mathematically challenged :) so it will help if you could share how exactly you do this. Many thanks once again. 

 
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"azuaro"Thank you guys...Glad to hear this has been helpful/interesting for some shooters...

Hi GLPalinkas:

If I understood you correctly, you are asking how to determine scope height? (Please correct me if I am wrong)

There are several ways of doing this pretty accurately...I personally use either of these two methods:

If I have the possibility of shooting the gun:
I put it on a rest, put a tiny dot on a target and place it in front of the gun, aim at the dot with the crosshair and shoot...The distance from the center of the hole of the pellet to the dot will be your scope height.

If I don't have access to shooting the gun:
Use calipers and measure from the bottom of the barrel to the upper tube area of the scope (Measure over the tube-not the turret), then measure the diameter of the barrel and diameter of the scope, add these two numbers and divide by 2...Finally, subtract this last number from first measurement (bottom of barrel to upper of scope) and this will be your scope height.

Note: Scope Height is an important number to plug into your ballistic program...This setting is usually determined by finding a comfortable position when shouldering/aiming your gun. Of course, we need to make sure that the scope height is enough for not running out of elevation adjustments at the distances we are shooting,
For longer distances taller rings/lower front rings combinations are generally used. 

Best regards,

AZ



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Exactly!! You understand correctly but I should have said "...for use in those programs".

I have used the first method and used tin foil (with a very small hole centered in the foil) over the objective lens, as detailed in the instructions but I always wondered if that was correct. I use both Strelok and Chairgun and your info really helps.
 
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Hello guys,

I read that the BC is different according to the speed of the pellet, and after that I found in a forum this table below, for JSB 18gr:


BC - Speed

0,030 – 173 m/s (567.6 ft/s)

0,036 – 216 m/s (708.6 ft/s)

0,040 – 250 m/s (820.2 ft/s)

0,032 – 274 m/s (899 ft/s)

0,027 – 295 m/s (867.8 ft/s)


And in the Strelok has the option to put a variable BC, or multi BC.

So I have a question, what BC you use for the JSB 18gr?


In the next week I will make some tests with my Matador, because I’ll be free of school and work!! =D


I’ll appreciate your help.

Thanks
Vinícius
 
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Checked out the weather flow thinking about buying the kestrol u have 5500 strelock said the 5xxx will be up and running soon think it will be more accurate I always hunting shooting different places elevations fluctuate between sea level and 5000 ft also rapid temp swings California desert to forest in a hour 
AZ
so did u ever get your kestrol 5500 to work with strelock will in automatically input your elevations temp ??? After messing with it couple times 
 
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Hello AZ
Sorry, I made 2 mistakes, I don’t read all you thread, I was at work, now I did, thanks for the great info.
And the second mistake is that the line of the BC is 0.27, the correct speed is 967.8 ft/s.
So the BC I am using now is this:

FT./Sec. B.C.
967 .027
899 .032
820 .040
708 .036
567 .030

And according to the shooting that I did yesterday it is really close I thing.
I zeroed at 55 yards and input all data into the StrelockPro, and the result is below, at 110 yards.
IMG_20151219_185808408_zpsjippljre.jpg
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This year I’ll buy my own chronographer, and try to get my measurements.

Thank again guys, I really appreciate you help.

Cheers,
Vinícius
 
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Vinícius;
Your figures look OK for your initial velocities, presuming best round head, balanced, pellets and changes in initial velocity related stability outcomes.
Here is a report I wrote 5 yrs ago after doing actual field testing at the stated ranges to show how AVERAGE computed bc may change over familiar ranges of 50 yd, 100, and 200 yards, when the initial mv velocity was kept constant. The bc change is of course reflecting the drag coefficient as indicated by the % velocity loss as the pellets progress down range. 
This is a tad different to varying the initial velocity (your case scenario) which also reflects the possible differences in initial and progressive stability relevant to the specifics of your table.
Over the years I, and others, have consistently observed the optimal bc of our best round nosed pellets as falling somewhere between 700 and 880 to 900 fps. 
10 m wadcutters move the optimal bc to somewhere in the high 500s fps, as I think AZ has implied; but the wadcutters lose out because the air flow around the pellet approaches speed of sound at a much lower actual pellet Mach number.
Anyway, enjoy the read as I think it was ground-breaking at the time. Best regards and Merry Christmas to you and AZ, Harry.
Late edit: note there are 3 pages of comments to click in the thread; see the little numbers 1 2 3 at the bottom. Some good discussion in there.
http://www.network54.com/Forum/79537/thread/1265721221/Experiment-+BC+changes%2C++with+range+and-+or+time+of+flight+and-+or+velocity-+Long-


 
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"azuaro""So optimal BC is measured in terms of what? …What does it mean to have an optimal BC? Does it mean that at that point is the most accurate point or does it mean that there is where the pellet is more aerodynamic or? …What I want to find out is how are we going to capitalize this optimal BC?
Is a “Better BC” desirable for flatter trajectory at the expense of accuracy, or vice versa? Aren’t we all after the most accuracy combined with the flattest trajectory and hunters may add the most energy? Lots of questions don’t you think?How and why is this happening? Is it that BC’s are really not really that important for accuracy or is it there something else that we need to discover?"



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AZ (?Alan Zazadney AZ?)
Later I shall respond to these questions either here or perhaps in another post after Christmas is over. It is Christmas Day here in OZ and a busy family time for me.
I shall respond to each of your questions; and where relevant, correlate them for you then.

On the issue of data collection though, these last 7 months I have collected my velocity decay data for each individual shot with Doppler radar, so Cd and then BC can be calculated without resort to the previous logistics of separate or combined chronographs; or of drop measures on targets or otherwise. .... 
I shall not forget. ........ Merry Christmas, Harry.
 
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