The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: General

Reply
 
Thread Tools Search this Thread
Old April 13, 2015, 06:44 PM   #1
screaming4vengence
Member
 
Join Date: September 5, 2014
Posts: 40
bullet stability question.

Over time I've seen many arguments about bullet stabilisation, but there's a lot of misinformation flying around so its hard to see who really knows what they are talking about.

So do bullets stabilize mid flight? Or is the most stable point the end of the muzzel? Or other?

Thanks for any replies. Hope this is in the right place
screaming4vengence is offline  
Old April 13, 2015, 07:00 PM   #2
Flapjack23
Senior Member
 
Join Date: January 12, 2009
Location: Yale MI
Posts: 163
As a bullet leaves the barrel it is affected by the motion of the barrel and the barrels harmonics. Soon after it becomes "stable", which is not to say that a bullet is unstable, it is just is no longer affected be a ridgid barrel. It takes a few feet to "settle down" which means it is only affected by wind and gravity. At some point velicity and spin is no longer sufficient to stabilize a bullet and it will upset meaning it will begin to tumble. This assumes a bullet does not hit something and upset prior to slowing down. Hope this helps.
Flapjack23 is offline  
Old April 13, 2015, 07:04 PM   #3
screaming4vengence
Member
 
Join Date: September 5, 2014
Posts: 40
So if someone said it takes 100 yards for a 338LM round to stabalize , they would be wrong because its really only a few feet from the end of the barrel?
Just a metaphorical , although I've seen that situation enough times that it borese.
screaming4vengence is offline  
Old April 13, 2015, 07:55 PM   #4
Flapjack23
Senior Member
 
Join Date: January 12, 2009
Location: Yale MI
Posts: 163
I would say that a bullet would not be unstable until it reaches the end of its travel. It is stabilized when it leaves the barrel, it takes some distance to allow gyrospic stability to overcome the effects of barrel contact and the bullet to settle down. It would never be "unstable" or inaccurate, and the effects of touching the barrel would likely not be noticable to the average shooter. Its mostly semantics. I would say that whoever said a 338LM round takes 100 yards to stabilize was wrong.
Flapjack23 is offline  
Old April 13, 2015, 08:09 PM   #5
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 6,869
Bullets are immediately thrown slightly off-kilter as they leave the muzzle due to gases escaping at the base.
In effect they are literally kicked in the a$$ just as they are set free.

This causes a slight but very high speed pitching/yawing at the start which gyroscopic forces cause to settle
down over time/distance as shown here;

https://www.youtube.com/watch?v=KH9SCbCBHaY
Berger animation


.
mehavey is offline  
Old April 14, 2015, 05:44 AM   #6
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
While bullets have gas escaping around their heel as they exit the muzzle, Sierra Bullets proved back in the late 1950's that hollow point bullets had more uniform heel dimensions and gas escaped most uniform around them. That's why they started hollow pointing their 30 caliber match bullets instead of making FMJBT ones. The benchrest community had known this for years and their hand made 22 and 24 caliber match bullets were hollow pointed as were Sierra's 22 caliber match bullets at the time.

The most common cause of bullets jumping off the bore axis as they leave is their unbalance. The centrifugal force of an unbalanced one spinning around 200,000 rpm to pull it off the muzzle axis is quite a bit for its size. While their outside dimensions may be perfect, the uneven thickness of the jacket an slightly off center lead core or extra tips puts their center of mass off the center of form axis. This is the reason it took bullet makers years to get uniform jacket material to make long and heavy bullets for a given caliber. A friend spun some Lapua match bullets in a collet spun by a Dremel Moto Tool while measuring the current drawn by it. The unbalanced ones drew more current; perfect ones the least. The perfect ones put 10-shot groups from .7 to 1.5 inches at 600 yards, the others inside 10 inches with few in the middle.

Even the most perfectly balanced bullets can be rendered unbalanced by crimping them in case mouths and starting them into the bore while they're very crooked in the case. Uneven rifling twists can also unbalance them in the bore as can leaving too fast from the case and slamming too hard into the rifling. So does sharp/rough edged case mouths scraping off jacket material seating them. Then there's a rough throat caused by uneven erosion that scrapes off jacket material more on one side of the bullet; it's unbalanced before it's all the way into the rifling.

Sierra's heavy 30 caliber HPMK's ruled the long range matches until better copper was available to make 28 and 26 caliber ones. 28 caliber HPMK's suffered first followed by 26 and then 24 caliber HPMK's. It wasn't until 10 to 15 years after the 7mm Rem Mag set a new 1000 yard record at the Nationals until consistent lots of 28 caliber, 168-gr HPMK"s were available. 10 years after that, 26 caliber HPMK's were available that shot as accurate as the 28 and 30 caliber ones.

Sierra's tests in their indoor ranges pretty much proved that all their bullets are stabilized by the time they're 100 yards down range. That aside, if any bullet's fired in a poor barrel, it may not stabilize until further down range then take the trajectory path it's on when it's completely stabilized.

Last edited by Bart B.; April 14, 2015 at 05:56 AM.
Bart B. is offline  
Old April 14, 2015, 06:42 AM   #7
tobnpr
Senior Member
 
Join Date: August 1, 2010
Location: Tampa Bay
Posts: 4,556
Bart,

Components on the way for a .338 LM.

I have read some "opinions" online from some that feel large, high BC bullets (like a 300 SMK) may not be fully stabilized at shorter distances (under 300M).

Dave Emary, Hornady's chief ballistic scientist, was quoted in an article as saying:

"It's not very common, but yes it is possible. It is primarily with heavy for caliber and long for caliber bullets or bullets that are grossly over-stabilized. In both of these cases it can take a long time to "go to sleep" or damp out all the "wobble" from the muzzle. Several cartridges that exhibit this behavior are the .338 Lapua Magnum and the .50 BMG."

Have you ever witnessed this, or do you have an opinion on this?
__________________
Remington 700/Savage Rebarreling /Action Blueprinting
07 FFL /Mosin-Nagant Custom Shop/Bent Bolts
Genuine Cerakote Applicator
www.biggorillagunworks.com
tobnpr is offline  
Old April 14, 2015, 12:34 PM   #8
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
tobnpr,

The key words are "over stabilized." Any such bullets take a while to settle down; especially the more unbalanced ones. No wonder that the smallest short range groups are shot with bullets spinning barely fast enough to keep them perfectly stabilized all the way to the target.

I don't think Sierra has problems shooting their 33 caliber 300-gr HPMK's into near 1/4 MOA testing them in their 200 yard range.

Nor do I think an unstabilized bullet that's a ways off the mean trajectory path will magically turn back into that mean path then stay there for the rest of its flight. Unstabilized bullets have more drag and lower BC's.

Last edited by Bart B.; April 14, 2015 at 01:16 PM.
Bart B. is offline  
Old April 14, 2015, 12:40 PM   #9
DaleA
Senior Member
 
Join Date: September 12, 2002
Location: Twin Cities, MN
Posts: 5,292
Once again I'm pretty amazed at all the information here.
DaleA is offline  
Old April 15, 2015, 05:32 PM   #10
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
I emailed my contact at Sierra Bullets. Hope to have their accuracy with 33 caliber 300 gr HPMK's shot from their test barrels in their 200 yard range.

Their software lists a Savage 116 with a 26" 1:10 twist barrel got best accuracy with 78.2 grains of IMR-4350 pushing the 300 HPMK out at 2650 fps.

Last edited by Bart B.; April 15, 2015 at 05:38 PM.
Bart B. is offline  
Old April 15, 2015, 08:11 PM   #11
Boncrayon
Senior Member
 
Join Date: March 24, 2008
Posts: 920
bullet stability question.

The rifling stabilizes the bullet as it leaves the muzzle. Air windage begins to destabilize the bullet as it spins toward the target.
Boncrayon is offline  
Old April 15, 2015, 11:06 PM   #12
Buzzcook
Senior Member
 
Join Date: November 29, 2007
Location: Everett, WA
Posts: 6,126
Quote:
The rifling stabilizes the bullet as it leaves the muzzle. Air windage begins to destabilize the bullet as it spins toward the target.
By stabilize we mean the bullet stops pitch and yaw relative to its line of flight.
The wind doesn't affect pitch and yaw, it affects position relative to the original line of flight. It pushes the bullet left or right.
Buzzcook is offline  
Old April 16, 2015, 08:56 AM   #13
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
Most bullets are not perfectly balanced. They jump off the bore axis when fired due to centrifugal forces pulling them that way. They'll wobble a bit more in flight for the first several yards before the stabilize. Match grade bullets with jacket thickness and core tolerances minimized are the best, but they all are not 100% perfect.

Just got email back from Sierra Bullets. Their tests with the 33 caliber, 300-gr. HPMK from both 1:10 and 1:12 twist barrels show its well stabilized at 100 and 200 yards. Don't know if they use the .338 Win Mag or the .338 Lap Mag for QC tests. Doesn't matter. If it's done with the Win Mag, it'll do a bit better with the Lap Mag.

Last edited by Bart B.; April 16, 2015 at 11:29 AM.
Bart B. is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 10:23 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.05326 seconds with 8 queries