I tired calculating my bc for jsb 18.13 using my vulcan @ 877 fps on average. I zero my rifle at 26 yrds and at 54 yrds one inch drop which gives me 0.056. Is this possible? And has anyone achieve this bc using the 18gr jsb
0.056 bc with jsb 18.13
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Wow thats impressive. i dont calculate this stuff i dont have a crony. but from research ive found crossman premier dome .177 is very good at .030 and HN baracuda at .035
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I tried calculating the b.c. on ChairGun using the drop method and the result made no sense when compared to others posted results. I went ahead and use the difference in velocity at two distances and got a b.c. of .0441 for the .22 cal. JSB 18.13 grain. Bill
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Hang on, I think I know this one, as I was misled in the same way when working out the BC of exacts in my Wildcat.
I also had a zero of somewhere near 26 yards, but when I look at the Chairgun trajectory, I realised that there was also the second zero that went with it.
The second zero was around 35 yards, and when I put that into the BC calculator, I got a more sensible result.
The true BC is worked out from the more distant zero as this will give the proper distance for pellet drop for the calculation.
So just put the second zero into the zero box and then Chairgun will get it right.
I also had a zero of somewhere near 26 yards, but when I look at the Chairgun trajectory, I realised that there was also the second zero that went with it.
The second zero was around 35 yards, and when I put that into the BC calculator, I got a more sensible result.
The true BC is worked out from the more distant zero as this will give the proper distance for pellet drop for the calculation.
So just put the second zero into the zero box and then Chairgun will get it right.
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That's why chrono's are invaluable. As you know I got 0.0441 for my JSB 18.13 so we are in the ballpark. Bill
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I think you have zeroed at 54 yd and get an approx POI 1.00 inches high at 26 yds.
My BC for 18.1 gr Exacts at similar MV is 0.034.
* with 54 yd zero I get approx 1.00" (1.09") high at 26 yd. That matches your POI (but as high at 26 yd not low at 54 yd). My sight height above bore is 1.8". There will be slight differences if sight height is otherwise.
* with 26 yd zero I get approx 2.3" (2.27") low of POA at 54 yrd .
* with a BC 0.056 and 26 yd zero you should be getting a drop of just on 2 inches at 54 yards..
To get only a 1 inch drop at 54 yards from a true 26 yd zero, the BC would be in the clouds CF clouds.
Perhaps back check your zero to see if it was 54 yd giving you a 1 inch rise at 26 yards.
Kind regards, Harry.
My BC for 18.1 gr Exacts at similar MV is 0.034.
* with 54 yd zero I get approx 1.00" (1.09") high at 26 yd. That matches your POI (but as high at 26 yd not low at 54 yd). My sight height above bore is 1.8". There will be slight differences if sight height is otherwise.
* with 26 yd zero I get approx 2.3" (2.27") low of POA at 54 yrd .
* with a BC 0.056 and 26 yd zero you should be getting a drop of just on 2 inches at 54 yards..
To get only a 1 inch drop at 54 yards from a true 26 yd zero, the BC would be in the clouds CF clouds.
Perhaps back check your zero to see if it was 54 yd giving you a 1 inch rise at 26 yards.
Kind regards, Harry.
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Hi Harry, just re check my trajectory looks like i have two zeroes 26 and 40 yrds and my scope height is 2.63"
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In that case a BC of 0.034 like mine would give you a drop from 40 yards zero to 54 yards of about one and a quarter inches . That all matches up fairly well with your extremely high scope center axis above bore line. The high scope mounting pushes the zeroes out further and can be very useful for keeping the pellet reasonably close to your line of sight. I like that set-up for certain things and mentioned it in a recent post. /topic/hold-under-hold-over-further-discussion/
So, put in your 40 yards zero, rather than 26 yd, and 54 yards target and see if it comes out at a bit over an inch drop with a BC of around 0.034. .... Hope this may have been helpful, Regards, Harry.
So, put in your 40 yards zero, rather than 26 yd, and 54 yards target and see if it comes out at a bit over an inch drop with a BC of around 0.034. .... Hope this may have been helpful, Regards, Harry.
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Hi All - I took crono velocities at two different locations and came to the conclusion that the BC of the 18.3gr was .0449 from my WildCat at 872 fps.
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Measured in my D460 with velocity at muzzle and again at 40 yards. BC for that pellet was 0.042. That was near sea level and in high humidity at around 90f.
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