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Old October 29, 2011, 10:41 PM   #26
jimbob86
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Horsefeathers.

Quote:
Boat tail bullets are pointed or Truncated cone which a large hollow point is not.
HORSEFEATHERS.

"Boat Tailed" refers to the back end of the bullet. While a pointed bullet does make for a higher BC, so does a ..... ahem, boat tail ..... two different design features, both decreasing the drag coefficient of the bullet.....

It is true that most (if not all) boat tailed rifle bullets have pointy noses (though many are pointy hollow point: "Open Tip Match" ring a bell?)..... but to say a hollow pointed bullet can't have a base that is narrower than the bullet shank is ignoring the fact that the XTP IS a hollow pointed boat tail. The bullet base is a smaller diameter than the shank..... this increases the BC of the bullet, and (I think more importantly) reduces the amount of bullet in contact with the barrel, reducing the coefficients of starting and sliding friction (See, Dr. Lutful Mannan, I was paying attention in Physics Class!)....
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Old October 29, 2011, 10:44 PM   #27
Jim Watson
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I stock up on the Hornady 147 RN boattails every time there is a "blem" sale.
I understand that the boattail is not for long range ballistics or for some effect on expansion of the other end, but to keep from bulging the brass when a long bullet is seated in a short case.
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Old October 29, 2011, 10:53 PM   #28
jimbob86
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That does bring me to another question. I always hear that .45 ACP is slower and won't over penetrate, but if you look at the FPS they list for some of the rounds, the difference is only 200 fps.
1. .....200 f/sec is huge when you are talking about an increase of 200 f/sec from 800 to 1000 f/sec: that 20%! That's like the difference between a 150 gr bullet in a .30/30 and a .30-06 (20% of 2800= 560...... 2800-560= darn near the 2300 f/sec a .30/30 launches a 150 grain bullet.....)

2. The .45 has much more frontal area than the 9mm to resist pentrating a target..... while a 9mm HP can hope to expand to .45" .... a .45 is already there.
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Old October 30, 2011, 03:45 AM   #29
xMINORxTHREATx
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Good point jimbob, I didn't take into account surface area. I was focused on velocity and mass, but I see why now.

And the reason I didn't think 200fps is that much difference is because my nephews paintball gun is 300fps and it's not exactly deadly, so I had it in my mind that 300fps isn't very fast. I forgot how much a paintball gun can hurt though.


I'm not arguing that a roundnose should have a higher coefficient than a hollowpoint, but in Hornady's manual, the 9mm with the higher coefficient is a 125gr HAP round, at .158 whereas the FMJ roundnose has a coefficient listed at .141 for a 124gr bullet.
Any thoughts? I'm assuming it's from what I mentioned early.
Quote:
because the concentricity of the bullet has a far greater effect at the tip than it does in the middle, and it's rather difficult to make a perfect tip
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