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Posted: 12/19/2004 4:28:17 PM EDT
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Ammo - Oracle claims M193 fragments out to 190meters. (207 yards) The Fragmentation Chart ,at the top of this forum, shows M193 fragments out to 130 yards. Both of these numbers are from 20 inch barrels. Which number is correct? |
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There are variables to consider with regard to the fragmentation issue. There is a grey area where the bullet may frag or may not. 2700FPS is basically the magic number. You can get consistent fragmentation from this speed. The grey area is from 2500-2700FPS, the bullet may or may not fragment. Below 2500fps, chances are slim. Hope this helps. |
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It's all about ballistic coefficient (BC). Per reloading manuals: Nosler 55 grain Ballistic Tip: .267 Speer 55 FMJBT, w/cann: .269 Hornady 55 FMJBT, w/cann: .243 Ammo oracle data assumed .267 Cd (coefficient of drag; I'm assuming this is synonomous with BC) Plugging in same altitude, humidity and starting velocity values in ballistics calculator, Speer/Nosler/Ammo Oracle BC maintains 2700 fps out to around 220 yds/200 m. Plugging in Hornady's BC maintains 2700 fps out to around 130 yds. Whose BC do you believe? |
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The source originally used for the Ammo Oracle is suspect; the ballistic calculator is no longer available. That's the reason we ended up with the thread that produced the new chart. Hopefully soon we'll get it integrated into the Oracle, but use the chart as your guide. Note that, as others said, even this new chart, which is based on much more reliable data, is still only an estimate. Environmental conditions alone can cause variations of + or _ 10%, and seemingly small variations in manufacturing can also have an effect, though this tends to be reduced with the match bullet loads due to the extra QC involved with making them. It is particularly a problem with SS-109 bullets, which vary quite a bit from lot to lot as well as from country to country. But the chart is still a good baseline, and the best information currently available. -Troy |
| BTW, the best way to determine BC would be to chrono some loads at the muzzle and determine actual muzzle velocity. Then put the chrono 100 yds downrange (be careful now) and chrono them again. Figure out the average loss in velocity over the 100 yds and you can play with ballistics calculators and plug in various BCs until you get one that matches observed data. |
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