ballistic coefficient on bullets

Michael Eichele

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GG,

You quoted:
[ QUOTE ]
On the flip side, a bullet that is overstabilized also has an altered bc because of the agressive yaw of repose and the nose might not follow the arc of the trajectory although it will be quite a small difference. Much smaller reduction in bc than if the bullet is understabilized of course.


[/ QUOTE ]

Leaving BC out of the picture, this very scenario you described here and what you have to say about it is one I have been criticized many times over for. So many shooter believe that that you cannot overstabilize a bullet, that it is either stable or it is not. The fact that it can be over spun is why I use as slow a twist as possible that will effectivly stabilize the bullets I wish to shoot. It is nice to see somebody else has finally agreed that a bullet can be over-stabilized. In a sense, you cannot overstabilize a bullet, but it can be spun to the point that it doesnt do you any favors elsewhere and can have a negative impact.
 

Desert Fox

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Dan Lilja wrote an article about this I believed on Sniper Country. He stated that when shooting a particular bullet, you must choose barrel with optimum (maximum)twist, just enough to stabilized that bullet. You get much better accuracy that way.
 

speadfreak

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And you guys wonder why the hell I don't give out any bc's on bullets that I make !!!!!!!!! /ubbthreads/images/graemlins/confused.gif
 

MagMan

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Richard, those of us who use them don't "wonder why" we know why. /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif
 

ss7mm

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Buffalobob

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KAPOW----------------------------------------------------------------------------------WHOMP, FLOP /ubbthreads/images/graemlins/grin.gif
 

goodgrouper

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If anyone ever rebuked you for stating that a bullet can be overstabilized, they obviously have never done much experimenting or reading. Just ask the legions of "black gunners" how much fun they had trying to get 40 grain vmax's to shoot accurately in their AR's. Even those guys find out eventually that they're just flogging a dead horse because a 1-8 or 1-9" twist just ain't gonna be kind to a 40 grain bullet. It is only because it is being spun a few more thousand times per minute that what it was designed to do, that's all!

This is a well documented principle of exterior ballistics. Dan's article is not the only good read. Sierra's most recent manual also has some good detailed info on the fact as well as Vihtavhouri's manual. Robert Rinker's "Understanding Firearm Ballistics" also has a great explanation.

It is better to have too fast a twist than too slow, but ideally, every bullet has a design spec window for rpm's and they shoot better when in that window.

Br guys are now ordering barrels with 13.5" twist because they shoot just a hair better than 14's. So they are custom tailoring a twist to their bullet so that it is not too fast or too slow.

Just throw that at the next guy who wants to tell you there is no such thing as overstabilization. /ubbthreads/images/graemlins/wink.gif
 

goodgrouper

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[ QUOTE ]
And you guys wonder why the hell I don't give out any bc's on bullets that I make !!!!!!!!!

[/ QUOTE ]

That is unfortunate. If everyone would just get it in their head that it is JUST A GUIDELINE for comparison and not scripture, then those of us who know that could run some trajectories for fun and see just what those long missiles would do. But as usual, a few boneheads ruin it for the rest of us. /ubbthreads/images/graemlins/frown.gif
 

ss7mm

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[ QUOTE ]
That is unfortunate. If everyone would just get it in their head that it is JUST A GUIDELINE for comparison and not scripture, then those of us who know that could run some trajectories for fun and see just what those long missiles would do.

[/ QUOTE ]

I agree completely. Normally I don't even respond to BC discussions but, I've never been able to understand the reasoning behind people's statements that they won't even try a bullet without published BC info.

If you know anything about bullets and their construction and the results of certain combinations then you can easily get started with the fun of what everybody should do, and that's test them yourself. I've never taken any published BC info as anything other than a starting point. If I don't have anything to start with I can come close enough to keep my feeble little brain happy until I do what I always do, and that is launch them down my barrel under my conditions and prove what they do, under all conditions at all ranges.

Then, and only then, I have a BC that applies to my equipment and under the conditions under which I tested them.

I would think that if you can spend thousands and thousands of dollars on guns, optics, travel for hunting and related equipment then you should be able to spend a few bucks on bullets to make sure that when you have that big buck/bull etc. in your sights in the fall that you know the bullet/cartridge/load combo you are using is the absolute best you could put together for your gun. But then I guess this logic would only apply if you aren't the type that shoots only 10-20 rounds a year and then goes "hunting". /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/grin.gif
 

Michael Eichele

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[ QUOTE ]
I've never taken any published BC info as anything other than a starting point.

[/ QUOTE ]

Thats about all a published BC is good for. A starting point. Also, the vast majority of shooters in general are never going to shoot past 400 yards anyway. It takes a pretty large error of a BC to drastically affect a 400 yard shot while a small amount of error is a clean miss on a deer at 1000 yards. Example: manufacture "X" publishes .500 for one of their bullets. You load em up and your computer tells you that at 400 yards you will be 28" low using .500 at your velocity in standard air density. 2550 MV. The reality is that your real world BC is .450 and the differance at 400 yards for the error is less than 1". Thats still a decent shot on a deer or a 2" bullseye for that matter. Move it out to 1K and.....its 38" off. Ooooops! Are they a good starting point most of the time? You betcha. Will they work at 1K without testing and verification, most of the time no as even a .010 error will result in a miss on a deer sized critter.
 

Ridge Runner

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Ok BC guru's, just so ya know I'm pretty misersble with algebra.
So, how do I figure actual BC? I have a ballistic program with options for "figure bc from velocity" and " figure bc from trajectory" does it matter which?
JS
 

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