 |  | | | |  | |  |  | Transonic Ballistics |  | |  |  | |
 Posted: Tue Feb 09, 2010 11:08 pm |
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| rsterne |
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| Joined: 15 Jan 2008 |
| Posts: 2998 |
| Location: Coalmont, BC |
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I ran across this description about the behaviour of Ballistics Coefficients in the transonic range on the Sierra website.... Although this information likely doesn't apply exactly to waisted pellets.... If certainly gives one reason to doubt the advisability of driving pellets near the speed of sound....
| Quote: |
| If the bullet starts at a velocity near 1300 fps, the ballistic coefficient is nearly constant until the bullet slows to about 1160 fps. At this velocity the ballistic coefficient rises abruptly as the bullet slows to about 1140 fps. Then the ballistic coefficient falls precipitously to a minimum value which occurs near 1100 fps. The ballistic coefficient then rises dramatically to a second peak value which occurs near 1050 fps. As the bullet slows below 1050 fps, the ballistic coefficient decreases in value, but in a less dramatic manner. |
They go on to say:
| Quote: |
| for bullets which travel with velocities in the transonic range, we have found that the following method is satisfactory. We use one value of ballistic coefficient for each bullet at velocities above 1200 fps (up to 1600 or 1800 fps). A second value is used for velocities below 900 fps. For velocities between 1200 and 900 fps, a ballistic coefficient value which represents an “average” for this transonic range is used. |
A further example of this is found in a BC chart for rimfire bullets found here:
http://www.exteriorballistics.com/ebexplained/22rimfire.cfm
I can't reproduce the chart here.... but I will give two examples:
.22 LR - 40 gr. solid: BC at under 905 fps = 0.192.... between 905 and 1047 fps = 0.169.... over 1047 fps = 0.145....
.22 Short/Long/CB - 29 gr. solid: BC under 905 fps = 0.139.... between 905 and 1047 fps = 0.122.... over 1047 fps = 0.105....
In my limited experimentation I have found DRAMATIC losses in the BC as the pellet approaches the transonic region.... with lighter pellets being affected more.... Some pellets lose nearly 100 fps in the first FIVE yards when fired just below the speed of sound.... 
Bob |
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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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