Bullet length ?

[r29l20]

Can someone explain to me why bullet "length" is important for a certain twist rate. I can understand bullet weight, but not length. Is it just that longer bullets are heavier and shorter bullets lighter? ???

[cat]

take a toy top like we all had as a kid see how easy it is to spin now try this with a pencil much harder same as a short and long bullet

[Eric in NC]

Totally length - weight has little to do with it.

Throw a baseball - easy to throw and get to fly straight. A football is a little harder but still pretty easy. Now try a baseball bat!

[319]

It is a lot easier to throw a javelin than a baseball bat though???

[Eric in NC]

Yes but that is because a javelin is forward weighted.

[319]

Hummm.....I must have been throwing a cheap javelin! So turn the bat around and throw the heavy end first?

[Eric in NC]

If the center of gravity on it wasn't around 1/4 of the length back from the tip, then yes it was a bad javelin (unless you are talking about an AMC Javelin of course - but if you can throw one of those...).

[319]

Yup, that settles it, it was a cheap Jav. It balanced out just in front of the grip. I would be very happy with just being able to slightly lift one end of the AMC!!!

So that just shows there is much more than "just" weight or length in the equation.

[anomad]

Can someone explain to me why bullet "length" is important for a certain twist rate. I can understand bullet weight, but not length. Is it just that longer bullets are heavier and shorter bullets lighter? ???


Length is a factor in how much of the bullet touches the inside of the barrel to engage the rifling. This is "bearing surface", some of the benchrest guys have fancy tools to measure that and sort their bullets by bearing surface.

Somewhere there will be a sweet spot for any caliber that combines bullet velocity, bearing surface, bullet weight, rate of twist and 89603978677 other variables.

[GaCop]

Longer bullets require a faster twist rate to properly stabilize them.

[Quickshot]

GACOP- I just recently experienced the condition you mentioned. Using 36gr. Varmint grenades in a slow twist Ruger #1. They shoot good. Now tried 50gr. VGs and at 100yd they hit the paper with a slight key hole. Out of my 1:9 Mod 12 Sav. both are stablized. Both are .223s. Yeah I know, get rid of the Ruger #1. I've tried to peddle it off for a couple of years, couldn't so decided to play with it some more. Quick

[Balljoint]

Try this site has articles that may help http://www.accurateshooter.com/articles/ look through has lots of info may boggle the mind

[GaCop]

GACOP- I just recently experienced the condition you mentioned. Using 36gr. Varmint grenades in a slow twist Ruger #1. They shoot good. Now tried 50gr. VGs and at 100yd they hit the paper with a slight key hole. Out of my 1:9 Mod 12 Sav. both are stablized. Both are .223s. Yeah I know, get rid of the Ruger #1. I've tried to peddle it off for a couple of years, couldn't so decided to play with it some more. Quick


You must have a 1 /14 twist, your stuck with the lighter bullets for the Ruger. If they shoot good, the Ruger will be a nice 300 yard rifle.

[GaCop]

Rugers have been very disappointing for me in the accuracy department. I had one of their stainless Model 77's, varmint weight barrel in 25-06. I never could get it to shoot better than 1 1/8" no matter what I did so I sold it. Same thing with a 30-06 Ruger International, most inaccurate rifle I've ever seen so dumped it too.

[Quickshot]

I believe the fore arm set up is the whole problem with the #1. I've been thru about all the suggestions in the pastyears and am not confident in it now though it seems to like the 36gr. V.Gs. Ruger triggers are a whole nuther story. For the origionator, I think you will find that one barrel may shoot anything you put in it and the next will be very particular, however it does appear that the long light weight bullet will need faster twist not necessarily because of weight but because of bearing surface. Quick

[helotaxi]

Bearing surface has nothing to do with stability either. Look at the two formulas for determining bullet stability, the Greenhill formula and the Miller index, and what variables go into those formulas. The only ones that are taken from the bullet itself are the diameter and the length. The ratio of length to caliber is the relationship that matters.

Bearing surface has an effect on the way that pressure builds in the chamber, more bearing surface means that more of the bullet is contacting the rifling and more friction from it moving down the bore. Examples of the irrelevance of bearing surface to stability are the Berger VLD bullets (very low bearing surface but very long, requiring a faster twist than similarly weighted bullets with a more conventional profile) and the Sierra .224 77gn MatchKing (relatively blunt ogive and a lot of shank and bearing surface but not requiring as fast a twist compared to even some lighter .224 bullets).

[tammons]

The spinning top analogy above is good.

If you have a short wide top you dont have to spin it as fast for it to stabilize.
If you have a tall narrow top, you have to spin it much faster.

As it applies to bullets coming out of the end of a barrel there is a sweet spot for
each particular bullet vs speed.

That said I had a 7 twist 223 that shot 52 gr amaxes tighter than any other 223 I have ever owned
and 7 twist is way fast for a 52 gr bullet.

IMO I dont think you can over stabilize a short light bullet, but you can spin a jacketed bullet so fast
that they blow up.

Same for extremely long jacketed bullets being pushed ultra hard.
Pushed too hard in a too fast twist barrel and it can actually deform or twist the bullet in the barrel, and those can disintegrate too.

Solid copper bullets dont have those problems.

I read about that scenario a while back.

A guy with a 22x47 Lapua pushing 90 gr bergers hard at like 3700 fps out of a 7 twist and he was losing bullets.

That did not work so he went to an 8 twist. Still to fast.

When he went to a 9 twist which originally he thought would not be fast enough, it worked.

[okie2]

Rugers have been very disappointing for me in the accuracy department. I had one of their stainless Model 77's, varmint weight barrel in 25-06. I never could get it to shoot better than 1 1/8" no matter what I did so I sold it. Same thing with a 30-06 Ruger International, most inaccurate rifle I've ever seen so dumped it too.

I have never had a bad Ruger 77 mkll varmit target rifle.
http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/308Savage10shots.jpg
http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/2506Ruger85grbtip.jpg
http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/85btip4064500gr.jpg
http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/85gr4831580gr.jpg
[http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/22040gr.jpg
http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/ruger2437-17-10.jpg
http://i661.photobucket.com/albums/uu340/OKIE2-photos/my%20guns/MY243ruger.jpg

[anomad]

Bearing surface has nothing to do with stability either. Look at the two formulas for determining bullet stability, the Greenhill formula and the Miller index, and what variables go into those formulas. The only ones that are taken from the bullet itself are the diameter and the length. The ratio of length to caliber is the relationship that matters.

Bearing surface has an effect on the way that pressure builds in the chamber, more bearing surface means that more of the bullet is contacting the rifling and more friction from it moving down the bore. Examples of the irrelevance of bearing surface to stability are the Berger VLD bullets (very low bearing surface but very long, requiring a faster twist than similarly weighted bullets with a more conventional profile) and the Sierra .224 77gn MatchKing (relatively blunt ogive and a lot of shank and bearing surface but not requiring as fast a twist compared to even some lighter .224 bullets).




You just explained why bearing surface is important.

[Eric in NC]

Nope - he explained why bullet length is important.