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7mm Mag ballisitcs?

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7mm Mag ballisitcs?

Old 12-04-2003, 05:55 AM
  #1  
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Join Date: Feb 2003
Location: Blythewood SC USA
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Default 7mm Mag ballisitcs?

I am very much a novice at interpreting ballistics and would like an explanation of how the velocity of a 150grn can be greater than a 140 grn. I compared the Winchester Supreme silvertips in 150 & 140 grn and found that the 150's velocity was greater than the 140 @100, 200 & 300 yds.
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Old 12-04-2003, 11:33 AM
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Default RE: 7mm Mag ballisitcs?

Evidently the 150 grain is loaded to a higher velocity either by a heavier powder charge or with a different powder. Are you basing your findings on chronograph tests you performed yourself or a chart put out by Winchester?

If both the 140 grain and 150 grain are loaded with lets say X grains of ABC powder, the 140 will always have a higher initial velocity out of the same rifle or test barrel. It's simple physics. Of course bullet design could cause effect things at longer ranges. A flat nosed bullet may shed velocity quicker than a HPBT due to air resistance.
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Old 12-04-2003, 12:14 PM
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Default RE: 7mm Mag ballisitcs?

Hi Back 40,

Initial velocity is of course the first factor to consider. And then of course bullet shape and composition. A bullet that weights more and starts slower than a lighter bullet started faster can still overcome the initial velocity advantage if the heavier bullet is more aerodynamic, (normally labeled as ballistic coefficient when dealing with bullets).

Another factor that some people do not consider is that even if the lighter bullet starts faster, and has an equivalent BC of the heavier bullet.....that at extended ranges the heavier bullet will still overtake the lighter bullet because of momentum. If they are both meeting the same air resistance, (and they are if the BC is similar), the mass of the heavier bullet provides momentum which will eventually overtake the less mass of the lighter bullet.

A good example. The .30-03 (later to become the .30-06 Springfield) was first fielded with a 220 round nose bullet. After Germany adopted a 150 grain spitzer for its 8X57 America adopted a 150 grain spitzer. It was found that the maximum range was in the vicinity of 3000+ meters for the new 150 spitzer. By adopting 170 (maybe 172...not exactly certain without looking it up) grain spitzer the maximum range was extended to 5000+ meters range. But recoil issues caused the U.S. military to go back to the 150 grain Spitzer. But the superior weight (momentum) had effectively increased the range over the lighter bullet.

You may ask, "well how does that effect me as hunter"? And I have to honestly tell you..."not much". But the lighter bullet which starts faster is NOT always the best bullet for long range shooting!

Hope this helps!
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