Bulet lenght question

[melloairman]

I was told today that a longer bullet is more stable than a short one if the twist is right . Not due to weight but lenght a lone . Is this true .Marvin

[MtGun44]

No. Longer is less stable, has to be spun faster to stay stable.

In the limit, a round ball is stable (if that still has a meaning) when not spun.

If you have aerodynamic effects on very long projectiles, the air can keep them
stabilized, like an arrow or bottle rocket (stick acts like a tail), but not in the
range of length to diameter ratios that you will find in bullets and boolits.

Bill

[melloairman]

That was what I thought . But I have been wrong before . And thought I would ask .Marvin

[fredj338]

With enough velocity, yes, the longer bullet will remain stable over a longer distance & be less affected by wind, but you have to get the velocity high enough to achieve that.

[GabbyM]

People get crossed up in there thinking and it becomes a n urban myth.

Long for caliber high B.C. bullets fired with proper twist rate at high velocity will remain stable and super sonic out to extreme ranges. That’s because of the high B.C. So then you get fellows saying things like long bullets are more stable.
But that’s only one third of the sentence they needed to state.

boat tail bullets are less stabel at short range. 22 caliber flat based Sierra 53gr MK rule out to two hundred yards and they are almost square compared to my 95 grain 6mm bullets.

[montana_charlie]

In the limit, a round ball is stable (if that still has a meaning) when not spun.
If you are saying what I think you are, I disagree with you.
CM

[MtGun44]

Stable, in the sense that it doesn't 'turn sideways', which, as I said, may not
even have a meaning when sideways is the same in all directions. The point is
that a round ball only needs a tiny bit of spin. Look at roundball muzzle loaders,
one turn in 60-70 inches or more. Short needs little spin, long needs more.

Bill

[PacMan]

The longest bullet that the guns twist can stablize properly with desired velocity will generally be the better bullet for hunting and longer distance work.

The other side is that a long bullet driven fast enough to stablize will penetrate deeper than a shorter bullet of the same weight. So in that sense it is more stable.

[NHlever]

The longest bullet that the guns twist can stablize properly with desired velocity will generally be the better bullet for hunting and longer distance work.

The other side is that a long bullet driven fast enough to stablize will penetrate deeper than a shorter bullet of the same weight. So in that sense it is more stable.

I agree with what you have said here except that I believe ( I am no ballistic expert) that shape has a lot to do with that too. A long for caliber boat tailed spitzer is apt to tumble when penetrating while a long for caliber round nose, or WFP will keep a straight path as the 7mm bullets that Bell used in Africa did. Again, not having a ballistics background, I sometimes compare a bullets flight to a football. The football, if thrown with a lot of spin can be touched in flight, wobble a bit, and then settle down to a straight path again while one thrown with minimum spin will be deflected off course with the same amount of interference. I also think that bullets fired through a fast twist barrel are perhaps better "brush cartridges" if there is such a thing. I also agree that boat tailed spitzers can be more stable at longer ranges than they are at shorter ranges before they "settle down". I have fired smaller groups at 150 yards with a very accurate .250 Savage than I could at 50 yards..... the limit of our range. Now all this is based on gut feeling, and observation over the years so it's not meant to be proven fact from me. Of course bullets fired through a fast for caliber twist will show more expansion too, and that has been proven. A short barreled Colt .38 Special will expand hollow points of equal weight, and construction at lower velocities than a S&W with it's slower 1-18 twist for example.

[HollowPoint]

So far everyone seems to have drawn their analogies and descriptions from "Long-Bullets." And you all seem to make sense. It sounds logical and it more than likely is.

Part of the original thing that melloroadman was told also had to do with shorter bullets being more unstable.

If we use the bullet pictured in melloroadman's moniker as a reference, I can see where the giver of this advise may have been coming from. Is there a possibility that this is what the "Giver of Advise" may have been eluding to?

When a short bullet such as the one pictured is close to the same, or larger in diameter than it is long, I don't know that any kind of rifling twist that will stabilize it for long; if at all.

An exaggerated analogy would be like trying to shoot a coin as if it were a bullet; with the edge of the coin as your driving-band.

Just a thought.

HollowPoint

[melloairman]

That we have come this far let me say thank you first . Now the conversation I had was not really with said bullet . But was talking about super sonic flight . But now let me narrow this down and say that I am now referring to just under super sonic . Around 1050 fps . Here is a 251 , 30.5 grain bullet that I shoot . Will not group at 850 fps . But will give better than moa at 1050 fps . It is .280 long . What brought the conversation up . Was I was thinking about upping my power and going super sonic . But I am having second thoughts about that . Twist is 1 in 16 .Marvin
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_6659A.jpg

[BAGTIC]

1. I once tried some perfectly flat cylindrical bullets .357 x .25 thick. If your bullet is shorter than it is wide it will definitely be unstable. Aerodynamic pressures will tend to turn the bullet alignment to conform to the least drag profile.

2. The reasons round ball shoot better when given a little spin is that most projectiles will rotate a little even when fired from a smooth bore. Problem is that it might not always be in the same direction or rate (knuckleballs). Having a little spin makes the rate and direction of spin uniform and helps to eliminate shot to shot variation.

[HollowPoint]

Marvin:

I'm not quite following you. How come you're having second thoughts? Is it because you're not sure if it will stabilize at higher velocities?

I say go ahead and load a couple and see what happens.

With a 1 in 16 twist and the correct alloy you should be able to drive them well above 2700 fps. I'm not sure what effects the bevel base on this bullet might give you but there's one sure way to find out. Give it a shot.

HollowPoint

[runfiverun]

he's using an airgun so it's a bit more effort than that.
the 1-16 should easily do 2600 ,but you will probably need a harder alloy to avoid stripping.
anyways a slower twist will generally favor a lighter [shorter] bullet.

[melloairman]

Yes I am using air for my gas . Have most my rifles just under the 1100 mark . Can go to 1300 - 1400 fps with a cost factor of about $200.00 - 300.00 . To get to above 2000 fps . the cost is going to be $1200- 1500 . From what I have seen in the Lyman reloader book about B.C. fps. and distance I wonder if it is worth the cost . It appears that with a muzzle velocity of 1600 fps at 100 yards most 25 -308 caliber bullets are at just over the 1100-1200 fps mark . Not much gain . Which means to get good accuracy at a further distance I need to get the muzzle velocity up to as close to 2500 fps as I can . Marvin

[HollowPoint]

Oh, an Air rifle. My mistake. Sorry.

That reminds me; I have an air rifle project that I've put on the back burner now that the weather's been so nice.

It's the testing of my new 45 caliber "Arch-Angle Bullets" and modifications on the Sam Yang 909 I acquired last year. I'll get back to it this summer when it's too hot to be trapesing around out in the desert.

HollowPoint

[melloairman]

Had a little work done on my 909 than you might like . Tuned to take fills right now at 2300-2400 psi instead of 3000 . Marvin
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_6769A.jpg
http://i301.photobucket.com/albums/nn55/melloroadman/909%20CHRONY%20READINGS/IMG_6778A1-12-11909.jpg
Not close to my Gargoyle .452 but it still is a good rifle .
Gargoyle low preasure valve .
http://i301.photobucket.com/albums/nn55/melloroadman/Gargoyle%20chrony%20readings/IMG_6662A.jpg
Gargoyle standard valve . I have a high preasure valve that I have not tested yet .
http://i301.photobucket.com/albums/nn55/melloroadman/Gargoyle%20chrony%20readings/IMG_6632AA.jpg

[Butcher45]

I have been hunting with my tuned SamYang 909 using the .45 EPP/UG which is .466 long. Barrel is 21.6 inches with a 1:20 twist rate. Velocity is around 870fps. I have gotten exit wounds with neck shots on coyote, and bobcat that indicate that the stubby EPP/UG maintained it's stability quite well.

An airgunsmith friend of mine gets groups right at 1 inch@100yards shooting the EPP/UG's from his own tuned 909S (refilling for each shot I believe).