SakoSteve270wsm
Handloader
- Apr 17, 2007
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Nosler,
Could you tell me what the BC for the 130gr E-tip will be please ?
Could you tell me what the BC for the 130gr E-tip will be please ?
NOSLER ???.....270 E-tip
- Thread starter SakoSteve270wsm
- Start date
- Oct 30, 2004
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Very close to .5 is my guess.
- Oct 30, 2004
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If you noticed the e-tip is longer than the BT. Additionally it is roughly 10% highr BC than the BT so if you do the math......
clearwater
Handloader
- Feb 5, 2005
- 505
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POP":94dc7gvy said:
Wouldn't the longer length make for more friction in the barrel, hence
slower velocities, IE no free lunch?
clearwater
Handloader
- Feb 5, 2005
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old #7":5455jvau said:
Wellll- isn't the bearing surface longer in this case, and the grooves
would be constant in a given gun.
Also how does density play in these bullets? Otherwise why wouldn't
we be using aluminum cores etc?
Some one correct me if I am wrong here.
The bearing surface doesn't have to be longer just because the bullet is longer.
Also the higher the BC the less velocity the bullet gives up down range.
You could have a bullet with a low BC and higher MV get passed up down range by a bullet with a high BC and a lower MV.
I can't remember how density is figured. I think it has to do with the length compared to the diameter. I haven't payed enough attention to it.
The bearing surface doesn't have to be longer just because the bullet is longer.
Also the higher the BC the less velocity the bullet gives up down range.
You could have a bullet with a low BC and higher MV get passed up down range by a bullet with a high BC and a lower MV.
I can't remember how density is figured. I think it has to do with the length compared to the diameter. I haven't payed enough attention to it.
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SakoSteve270wsm
Handloader
- Apr 17, 2007
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Your right Old #7 accept SD is weight and diameter,thats why all .270 130gr bullets have the same SD ect ect.Don't know the exact formula. :lol:
clearwater
Handloader
- Feb 5, 2005
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I am not talking about sectional density, and BC is dependent on shape.
I don't see how given same shape, but longer,you get higher BC. Seems
like barrel and air friction would give it a lower BC.
I don't see how given same shape, but longer,you get higher BC. Seems
like barrel and air friction would give it a lower BC.
- Oct 30, 2004
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old #7":lt4irimw said:
correct
Sectional density is mass/diameter squared.
G
Guest
Guest
clearwater":1vpoil55 said:
Barrel friction has no impact on BC, as BC is a measure of how the bullet flies, and once it's flying, barrel friction has no bearing. Think of it like the friction of the wheel bearings in a car as it rolls along having nothing to do with the aerodynamics of the body shape. As for wind resistance, BC is still just a measure of aerodynamic efficiency. A longer bullet of the same diameter, ogive and heel shape, will offer the air going around the bullet more time to stabilize between being displaced outward around it, and displacing back inward behind it. More time to stabilize means less overall air resistance (as air friction is really nil considering the minimal surface area versus the velocity). I hope that helps a little. I'm not an engineer, but I did stay at a Holiday Inn Express last night...
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SakoSteve270wsm
Handloader
- Apr 17, 2007
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BTT
clearwater
Handloader
- Feb 5, 2005
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If a longer bullet has greater friction, both air and in the barrel, it will
have a slower velocity or higher pressure.
Hence an all copper bullet will develop lower velocity compared to a
denser material.
This may offset gains in BC.
Second part of my question, how does a longer bullet have a higher
BC than a shorter one if they weight the same, assuming similar shape? Seems like the longer bullet would be more affected by air resistance.
have a slower velocity or higher pressure.
Hence an all copper bullet will develop lower velocity compared to a
denser material.
This may offset gains in BC.
Second part of my question, how does a longer bullet have a higher
BC than a shorter one if they weight the same, assuming similar shape? Seems like the longer bullet would be more affected by air resistance.
G
Guest
Guest
Again, air resistance is fairly minimal compared to the drag produced as a bullet displaces air and then that air flows back into the flightpath behind the bullet. Aerodynamics is really what we're talking about here, and an object can have a very low coefficient of drag (cd) and yet be a large object with more surface area than a smaller object. Compare an airliner to a volkswagen sometime, and you'll understand what I mean. That comparison is still not completely valid though, because in both cases, we're talking about an object under power, while a bullet in flight is a glider of sorts. A longer bullet produces less turbulence, and thus is more aerodynamic (higher BC) and will fly more efficiently (shed speed slower).
As for the friction aspect, a bullet with a longer bearing surface will create more friction (resistance) coming down the barrel. This can actually increase velocity, however, by lengthening the time in the barrel, and therefore lengthening the time under acceleration. What this means, from a pressure standpoint, is that the pressure curve will be elongated, meaning there is greater area under the curve, and thus greater velocity. Now, the problem can arise that a bullet of a given shape can create enough friction to cause pressure to spike at an earlier time, and then you might end up with a lower powder charge and a smaller area under the curve overall. It will vary a lot with numerous variables, but I think you see the idea can go either way. With the right powder (a slower one, in many cases) you can overcome resistance and create that longer barrel time, which equates to larger area under the curve, which equates to greater velocity.
Man, these Holiday Inn Expresses are terrific!
As for the friction aspect, a bullet with a longer bearing surface will create more friction (resistance) coming down the barrel. This can actually increase velocity, however, by lengthening the time in the barrel, and therefore lengthening the time under acceleration. What this means, from a pressure standpoint, is that the pressure curve will be elongated, meaning there is greater area under the curve, and thus greater velocity. Now, the problem can arise that a bullet of a given shape can create enough friction to cause pressure to spike at an earlier time, and then you might end up with a lower powder charge and a smaller area under the curve overall. It will vary a lot with numerous variables, but I think you see the idea can go either way. With the right powder (a slower one, in many cases) you can overcome resistance and create that longer barrel time, which equates to larger area under the curve, which equates to greater velocity.
Man, these Holiday Inn Expresses are terrific!
nicely stated dubyam
take a look at a 50 cal B.C compared to a 22 cal.
The bigger and longer bullet has a higher bc than the little one for the exact reason dubyam stated.
3000fps with a 750gr 50cal bullet that has a high B.C. (Hornady has one in the low 1's 1.1 and change) will fly flatter and farther than a 22 cal leaving the barrel at 4000fps.
It's all about efficiency.
take a look at a 50 cal B.C compared to a 22 cal.
The bigger and longer bullet has a higher bc than the little one for the exact reason dubyam stated.
3000fps with a 750gr 50cal bullet that has a high B.C. (Hornady has one in the low 1's 1.1 and change) will fly flatter and farther than a 22 cal leaving the barrel at 4000fps.
It's all about efficiency.
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- #18
SakoSteve270wsm
Handloader
- Apr 17, 2007
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Guess I am not going to get an answer. :?
A
Anonymous
Guest
B.C. for the new E-Tip is .459. Sorry for waiting so long to answer, I just wanted to make sure that all the information that I give everyone here is 100% correct.
