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Anyone know … What the BC value is running on JSB .20 15.89 HEAVY pellets ?  

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Motorhead
(@motorhead)
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Posts: 114
July 30, 2020 20:06:28  

Searching the web and finding nothing ... JSB factory site has nothing either.

 

help if you can ... thanx

 

Scott S


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Hector J Medina G
(@hector-j-medina-g)
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July 31, 2020 08:31:50  

Scott;

As long as you are shooting them at under 875 fps, it will be a bit above 0.035 from a good barrel.

The greatest enemies of these pellets' BC are shooters that insist on using them at high velocities.

Of course, the specific conditions of your system will determine your outcome.

HTH

 

 

 

HM


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Motorhead
(@motorhead)
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July 31, 2020 11:37:27  

This inquire was to get some idea from others if or not the heavier 15.89 would likely show an improved BC over the 13.7 grain .20 cal ?

In my testing and getting chairgun data to follow actual field ballistics of the original JSB Exact 13.7 when shot at @ 800 fps, found time & time again the BC value needed to be raised to @ .040 for lower elevation and .044 when at @ 5000' * BC corrected from the IIRC @ .032 default BC value provide by chairgun.
Doing so the DATA produced by chairgun is Dead Nuts accurate !!

To stay under 20 FPE for Field target work with the 15.89 grain, velocity will need to be 750 fps and no faster. This speed reduction from a previous 800 I'm sure will shift the BC value some as well ???


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Hector J Medina G
(@hector-j-medina-g)
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August 1, 2020 10:14:33  

Yup!

Drag goes with velocity, so BC goes inversely to velocity in this region (If velocity drops, BC will rise). I wouldn't be surprised if, at long ranges (over 60 yards and slower velocities), your BC did not approach 0.05. At the higher speeds (875 fps), BC could drop as low as 0.035, what you are using is some sort of "weighted" average.

Truth is that Chairgun, by using ONE single BC cannot be "dead nuts"  at ALL ranges. You need to use a software that uses BC's by sections. One of the reasons why Chairgun is no longer an active piece of software.

Don't think that you would benefit from the shift, because at 16X max you are more challenged by range than by wind; though I am sure it would be interesting to test.  😉

Keep well and shoot straight!

 

 

 

 

 

HM


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Motorhead
(@motorhead)
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Posts: 114
August 1, 2020 11:32:39  

Yes RANGE estimation and accuracy of it is paramount.   At 16X as a Hunter shooter those final 15 yards can be a real bugger.

Not unlike WFTF shooters with 8.4's @ 800 or 10.3's @ 720 the velocity of a .20 cal in 13.7 or 15.9 is very similar at @ 800 & 740.  Sadly without the higher magnification afforded to the Hunters that WFTF has, we in hunter are at an even bigger challenge as we slow down shooting speeds with heavier pellets chasing improved wind drift tendencies.  

 

.20 cal for a few of us out west has been a real advantage ( We get wind ! ) over most of the folks shooting the .177's.    It is an undisputed fact there are some with .177's that have no problem shooting with or at times beating those with the .20's ..... But would say on average shooting a tad heavier & slower pellets with good D.O.P.E. has advantages in open space with breeze over a fast and flat LIGHTER pellet.

 

Like a Wheel or a Mouse Trap there are many ways to implement either ... only accepted compromises dictate which is chosen ... Loosely anyways.

 

Scott S

 

 

 


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