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  #1  
Old 09-05-2007, 01:22 AM
GLWenzl GLWenzl is offline
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Default Bullet bearing surface/bullet design

Just curious????

For example, say you make two bullets the same weight & type (and the same caliber) but the one bullet with a longer bearing surface…. Have you seen where the longer bearing surface gives greater accuracy than one with a shorter bearing surface???

I know they are different weights but like a 33 vs 32 grain V-Max???

How bout a 17 gr V-Max with its longer surface (for its size) anything do with it’s inherit accuracy for the HMR (and CCM)???

Lastly BTs??? I have read that makes no difference out to 300 yards but has anyone really tested this out? I here now that it may no make any difference out to 500 yards…

I realize there are plenty of programs that will spit out all kinds of data on the BC of the BTs but am really more interested in real life experiences…
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  #2  
Old 09-10-2007, 08:08 PM
tim simbari tim simbari is offline
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Ed Watson, who passed away this last year, made great BR bullets and would make the same weight bullet on 2-3 different lenght jackets. There was no hard or fast rule, some bbl's liked one or the other. He had told me once that it had more to do with the center of mass than the bearing surface per se.
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  #3  
Old 10-03-2007, 07:45 AM
303Guy 303Guy is offline
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The question I would ask is does a longer bearing surface make the rifle more forgiving of poor bullet alignment? There are rumours that round nose bullets can be more accurate. Is that due to centre of mass/centre of form or longer bearing surface? The most accurate bullet I have tried is a 45gr Super-X 218 Bee bullet. It is a round nose hollow point and is quite short. It out shot the Hornady match bullets I was using in my mini-14. 3/4 MOA against 1 MOA groups out of a mini-14! The Hornady bullet has a longer bearing surface but the bearing surface to bullet length ratio is less than the 218 Bee.
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  #4  
Old 10-03-2007, 12:34 PM
rstreich rstreich is offline
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Gary, here's what I've read not what I know: Flatbased bullets tend to be more accurate than boattailed bullets simply because it's easier to make the base of a flatbased bullet nearly perfect. If the base of the bullet releases gases unevenly, the bullet will be deflected as it exits the barrel. However, if the base of a boattail is as good as the base of a corresponding flatbased bullet, then the boattail will tend to be more accurate than the flatbased bullet because it has a higher BC and will be deflected less by minute changes in the wind. (Since the shape of the ogive also affects BC, this assumes that the two bullets have the same ogive.)

Having a higher-BC bullet can help at any range, it just depends on the conditions. If it's a relatively calm day, the difference between the two might be too small to notice. But, as the wind picks up, you'll start to notice less deflection with the higher-BC bullets.

As to the effects of longer bearing length, I've never seen anyone suggest that a longer bearing surface makes a bullet more accurate. It could reduce in-bore yaw as 303Guy suggests, but I kind'a doubt it. There's enough force behind a bullet to swage a bullet into just about any shape, so I don't think it could help realign something that it out of alignment, but I don't know for sure. I do know that the long-range BR guys sort their bullets by bearing surface to ensure that they only shoot groups with the same length bearing surface.

I don't think round-nose bullets are more accurate than others. My only evidence for this is that if they were, every short-range BR guy in the world would be using them. If one guy started winning matches with a round-nose bullet, at least half of them would switch bullets overnight.

There's a lot of "think" and "tend" in this reply, but from what I've gathered no one really knows the answers to questions like this. The only facts seem to be statistical correlations of results. About the only thing that seems to be known for certain is that different barrels like different combinations of components and you need to use the one that works.

robert
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  #5  
Old 10-03-2007, 04:26 PM
iiranger iiranger is offline
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Default Ask Corbin(Dave)....

In the discussion of the rebated boat tail (over the regular boat tail) he cites a lengthy study, probably military, but government funded and probably done by the best science/equipment available at the time. As I recall:

Big consideration is the length per twist. The spin will stabilize, but if it is closer for the bullet length, less time/yaw/ etc.

Obviously the boat tail adds length without adding bearing surface. Good? Bad? It goes back to basic twist to start. There was a time when the "up to date" shooter had a .308 with a 1 in 11 twist...

Mr. C argues that the boat tail is wasted on calibers .24 and below.

And it only "kicks in" at long distance, actually when the bullet has slowed to below the speed of sound... With a magnum that is probably a distance aa average shooter should not be shooting at game...

Dave takes questions... corbins.com... if you want the science... luck.
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  #6  
Old 10-04-2007, 02:16 AM
GLWenzl GLWenzl is offline
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Thanks for all the replys guys.... Somedays I get to think'n too much but it sure seems interesting that the short bearing surface on the 17 gr HMR bullet works real well and the older 33 gr V-Max that everyone seemed to have super luck with just made me wonder about it some???

Been working and on the run too much as of late to give this kind of stuff much thought! Bout made my head hurt just thinking about it tonight! LOL
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Old 10-04-2007, 10:10 PM
Bryce Bryce is offline
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Boat tail and speed of sound. That is my understanding as well.

Look at aircraft.

Subsonic flight - rounded at the front and pointy at the rear.

Supersonic flight - pointy at the front and blunt at the rear.
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  #8  
Old 10-07-2007, 11:49 AM
harrens@adelphia.net harrens@adelphia.net is offline
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Default Supersonic

Not only that, but consider the RPMs those planes are turning.
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  #9  
Old 10-10-2007, 05:49 PM
303Guy 303Guy is offline
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It is likely that the RN accuracy suggestion arrises from the use of cheaper bullets and guns with long throats and bad bores. All else being equal, the RN bullet would not 'buck' the wind very well.

GLWenzl, the statement "that it may no make any difference out to 500 yards…" would probably be true to a target shooter. The calculations show that the difference at say, 200yds, is quite small really. Theoretically, a BT would extend my Point Blank range by 10yds. (My definition of point blanc might differ from another’s - bullet deviation from line of sight less than 45mm, scope hight 50mm).
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