8,4g vs 10,3g ballistic
Why FT shooter use 8.4g pellets and not heavy 10,3 g?
The standard answer is that the 8,4g pellets have much flatter ballistic curve, which is true.
But this reasoning seems not justified. Let me explain:
I take my Anschutz 8002 for example: 15.5 joules, zeroed at 25m, scope height 75 mm.
1) Exemple: with 8.4 grains jsb exact, zeroed at 25m, 15.5 joules
- A range of 50 m needs 39 clicks (69,2mm)
If I do an range finding error about -2 meters: 48 m estimated instead of 50m, this error correspond to 5 clicks, so I shoot 11.8 mm too low
If I do a range finding error about +2 meters, 52 m instead of 50m this error correspond to 6 clicks, so I shoot 13.1 mm too high.
2) Exemple: with 10.3 grains jsb heavy, zero to 25m, 15.5 joules
- A range of 50 m needs a correction of 50 clicks (88.3 mm)
If I do a range finding error about -2 meters: 48m instead of 50m, this error correspond to 6 clicks, so I shoot 13.9 mm too low.
If I do a range finding error about +2 meters: 52m instead of 50m error is 6 clicks, so I shoot 14.9 mm too high.
In summary: for a range finding error about 2 m there is no significant différence of the correction between 10.3's and 8.4's.
11.8 to 13.9 mm = -2 mm for an estimate of 48m instead off 50m
14.9 to 13.1 = 1.8 mm for an estimated 52m instead of 50m.
I find that a range finding error of 2 m at 50m whatsoever with "jsb exact" or "Heavy jsb" leads to the same error (approximately 2 mm).
Now look at the wind drift for these two pellets weights:
1) For a wind of 5km/h at 90 °
The drift is 35 mm with "heavy" so what is 49 mm with jsb exact
2) For a wind of 10 km/h at 90 °
The drift is 70 mm with "heavy" so what is 94 mm with jsb exact
If I summarize, the JSB Exact derived from 14 mm more than the Heavy under the influence of a wind 5km / h (24 mm for a wind speed of 10 km / h).
For a wind from 0 to 5 km/ h if I do not correct my sight the target fall, while this is not right with the "Exact".
So JSB EXACT 8.4g or HEAVY 10.3 g ?
That is the question.
Last edited by flyfisher; 4th November 2014 at 08:27 PM.
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