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New Barnes bullet testing.....

 
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  #15  
Old 02-20-2011, 03:19 PM
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Re: New Barnes bullet testing.....

Buckbrush,

I can not say for sure but I do know they got their rears handed to them when they came out with inflated BC numbers with the TSX bullets. They really got a bad rep for that and many hunters kind of turned their backs on them and their bullets.

Perhaps this time they think that maybe if guys figure out that the actual BC is much higher then advertised numbers that they will feel like their getting something for nothing.

If in fact they are higher then advertised, it will only add to the work needed to figure out an accurate BC. It would be better if they just did not offer any ballistic data if they are not going to release accurate BC numbers.
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Kirby Allen(50)

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  #16  
Old 02-20-2011, 04:37 PM
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Re: New Barnes bullet testing.....

Quote:
Originally Posted by Fiftydriver View Post
Barnes lists them as having a BC of roughly .570. In all honesty, this is a mystery to me. Here is why. When I set this new bullet next to a 300 gr SMK with a BC in the .800 to .820 range when fired from my 338 Allen Magnum, the first obvious difference is that the TTSX bullet is roughly 0.075" longer.
It's because it lacks the weight. It needs weight. Not length. Weight. To match the SMK's BC it would need a much better shape than the SMK to make up for its lack of weight.
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  #17  
Old 02-20-2011, 04:42 PM
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Re: New Barnes bullet testing.....

Quote:
Originally Posted by Jon A View Post
It's because it lacks the weight. It needs weight. Not length. Weight. To match the SMK's BC it would need a much better shape than the SMK to make up for its lack of weight.
+1.

Sectional Density, form factor and velocity.

Many shooters have the idea that length in and of itself = higher bc's. It is that longer bullets for a given weight typically have better form factors that makes for the higher bc's. Pure copper bullets given the fact that it takes more material to make them have a given weight versus a lead core bullet will be longer. This allows for the possibility of a better form factor/bearing surface relationship.

M
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Last edited by Michael Eichele; 02-20-2011 at 05:14 PM.
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  #18  
Old 02-20-2011, 05:06 PM
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Re: New Barnes bullet testing.....

I am sure there is some trueth to that for sure but please explain this to me.

How do the new 142 gr SMK in 6.5mm offer the exact same BC as the longer and heavier old 155 gr SMK design?

How do the 265 gr AT RBBTs from the old wildcat company produce a BC in the .88 to .90 range compared to the 300 gr SMK at .78 to .8?

I am not trying to pick any fights in any way. I believe what you say but I also know for a fact that there are certain situations that fly in the face of these theories, just curious what your opinion is of why that is?

Also, there are several companies that offer bullets that simply have the same jacket and OD specs but simply have a lighter lead core. BC values may certainly be less but they are generally within the 0.02 to 0.04 range compared to the heavier bullets.

Another example, take any bullet and compare its design with an open HP to that of a tipped design, bullets of identical weight, BT design, ogive design. Only difference is length, which will have a higher BC?
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Kirby Allen(50)

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  #19  
Old 02-20-2011, 05:46 PM
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Re: New Barnes bullet testing.....

See bold below:

Quote:
Originally Posted by Fiftydriver View Post
I am sure there is some trueth to that for sure but please explain this to me.

How do the new 142 gr SMK in 6.5mm offer the exact same BC as the longer and heavier old 155 gr SMK design?

I will admit that I am not familiar with this 155 so take this opinion with a grain of salt. It seems like maybe a form factor?

How do the 265 gr AT RBBTs from the old wildcat company produce a BC in the .88 to .90 range compared to the 300 gr SMK at .78 to .8?

Better form factors

I am not trying to pick any fights in any way. I believe what you say but I also know for a fact that there are certain situations that fly in the face of these theories, just curious what your opinion is of why that is?

Also, there are several companies that offer bullets that simply have the same jacket and OD specs but simply have a lighter lead core. BC values may certainly be less but they are generally within the 0.02 to 0.04 range compared to the heavier bullets.

Another example, take any bullet and compare its design with an open HP to that of a tipped design, bullets of identical weight, BT design, ogive design. Only difference is length, which will have a higher BC?

The one with the tip provided the meplat is smaller than the one with the hollow point. You would not think there would be much of a difference but there is. Years ago I opened up the hollow point on the 190 SMK to the point where the meplat was about .010 larger than factory (if my memory serves me correctly) and lost a ton of BC value. It tuned a 190SMK into a .450ish bullet. It illustrates that form factor plays a huge part.

These are just some ideas that support the idea of sectional density and form factor making up the bulk of a BC value.

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  #20  
Old 02-20-2011, 06:07 PM
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Re: New Barnes bullet testing.....

M.E.

That is certainly true, a larger Meplat certainly drops BC values, no question there. I am not well versed in form factor so do not have much to offer there. I just build rifles, not bullets.

That said, if you take two identical bullets, same weight, same dimensions, put an aluminum tip on one and leave the other as a HP, the length of the AT bullet will be MUCH longer then the HP and the resulting BC will be dramatically higher.

You can go with your theory that its because of the meplat diameter, I can say its because of the added length...... In the end it could be either or both but both certainly effect BC.

Its similiar to the arguement that a larger caliber will drive a bullet of the same weight faster then a smaller caliber bullet of the same weight when used over the same case capacity.

Some will say that its because of the increased area of the bullet base so more force is applied to the base of the bullet per sq. inch.

Others, including myself will say its because of baring surface being much less with the shorter, larger diameter bullet and the ability to use faster burning powder.

Again, parts of both are theories are likely correct but its a fact that both have a part to play in the velocity potential between two calibers with same bullet weights.

Back to the bullets. Lets look at the Hornady 208 gr match bullets. The A-max with the tip has a BC of .650, the standard HP has a BC of .620... Yes the meplat is finer for the tipped bullet, yes the length is longer for the tipped bullet, in the end, the bullets weight the same, likely have very similiar form factor and yet the longer bullet has a higher BC.

Also the 180 gr Hornady SPBT and Interbond. The SPBT has a BC around .450, the tipped bullet in the .480 range. Yes finer meplat, yes longer bullet, higher BC same bullet weight and design.

Simply put, you take a certain bullet weight, no matter the bullet weight, if you add a tip for a fine meplat, use an aggressive ogive design, good boat tail design you will get the longest bullet possible for that bullet weight no matter what the bullet material is made of.

Again, I fall back on the comparision between the 300 gr SMK and the 265 gr AT RBBT wildcat bullets. The Wildcat is MUCH lighter and much longer and with a finer meplat. All of which adds up to a much higher BC bullet with the ability to be driven much faster then the heavier bullet as well.

Form factory certainly has alot to do with BC value but I still stand by the point that a longer bullet will always match of exceed a shorter bullet in BC. Now if we used a long aluminum bullet that weighted DRAMATICALLY less then a lead core bullet I would certainly believe that momentum would be dramatically difference. In the case of the bullets we are talking about, it will be very minimal. I am sure its there but in a very limited role.

Again, not flaming in any way, just saying that the resulting BC value is likely determined by both theories in conjunction with each other, not one apart from the other.
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Kirby Allen(50)

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  #21  
Old 02-20-2011, 06:33 PM
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Re: New Barnes bullet testing.....

Kirby, it's not theory. It's the way it works. If you increase the length of the nose, that improves the form factor. That is completely different from increasing the length of the shank (bearing surface part) for a certain weight because the bullet has no lead in it.

You said the nose was the same length as the SMK and the boattail was shorter. This means the overall length is due to a long shank which will not help its BC at all.
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