tumbling bullet? what the heck?

Originally Posted By: baltz5262800fps 105vld 1-8" twist. 3300fps 105vld 1-9" twist should stabilize JMO

Can a 6mm Rem get a 105 grain bullet to 3300 fps? Otherwise your numbers should help those in denial that it takes a 500 fps increase to stabilize in a 1:9 barrel vs 1:8. Of course I am not endorsing those numbers without research.
 
Originally Posted By: dogtiredOriginally Posted By: baltz5262800fps 105vld 1-8" twist. 3300fps 105vld 1-9" twist should stabilize JMO

Can a 6mm Rem get a 105 grain bullet to 3300 fps? Otherwise your numbers should help those in denial that it takes a 500 fps increase to stabilize in a 1:9 barrel vs 1:8. Of course I am not endorsing those numbers without research. My speer book lists one 105gr load at 3145fps out of a 1-9" 22" barrel but there bullet is a flat base. 26" barrel and some testing might just get close to 3300. but I have my doubts. The 105 vld is a specialty bullet, designed for custom rifles. The 18" remington mod 7 243 youth, i pack for predators once in awhile is not going to shoot them.
 
2muchgun has it exactly right.

The 105g Berger VLD with it's much longer than normal secant ogive nose moves the center of pressure farther ahead of the center of mass than other bullets of the same weight and therefore is a harder bullet to stabilize. That means it takes a faster twist barrel than a more conventionally shaped bullet of the same weight.

Take, for example (because I have data on that bullet in "Applied Ballistics For Long Range Shooting" by Bryan Litz (HIGHLY RECOMMENDED book for those who like to hit what they shoot at) the 6mm 95g Berger VLD. For a long time the standard twist for .243 barrels was 1:10". My Savage had 1:9.25 from the factory as I recall, but even today some barrels are 10" twist (the barrel on my Savage at the moment is a 1:10" twist). The 95g Berger VLD won't stabilize adequately in a 1:10 barrel but the 95g Nosler BT will (I know the nosler will stabilize because it works great in my 10" twist .243) - the gyroscopic stability factor (Sg)for the 95g VLD in a 10" twist barrel is 1.07 at 2815 fps. In a 1:8 twist barrel @ 2815 fps the Sg is 1.7 for that bullet. Berger recommends a minimum 1:9 twist for the 95g bullet (a difference of 1").

Sg values between 1.0 and 1.4 are marginal - drag will be higher and the bullet may exhibit strange behavior. Anything less than about 1.4 should be avoided, especially in a hunting rifle.

Berger recommends 1:8 twist for the 105g VLD. If 1:9 would work, trust me on this, they would recommend 1:9 because there are a heck of a lot more 6mm rifles with 1:9 twist than 1:8 twist. More rifles = more market. I have an 6mm 8" twist Shilen Match barrel on my shelf to be chambered in .243Win specificaly to make a barrel that will shoot the Berger 105g VLD because that bullet is "not" stable in my 1:9" barrel. The math says 1:9 won't work, experience says 1:9 it won't work. both the math and experience (most 6BR rifles have an 8" twist to shoot the Berger bullet) say 1:8" works. That one (1) inch makes "all" the difference.

Physics is physics, mother nature cannot be fooled, and we aren't going to drive a 105g bullet fast enough to stabilize it (Sg equal to or greater than 1.4) in a 9" twist barrel with out significant over pressure issues or a barrel of truly alkward length. I found a 109% compressed load in QuickLoad that would get to the required ~3,300 fps but the peak pressure would be just over 80,000 psi - that's 1/3 more than max! Don't do that.

The other way to get to that required muzzle velocity is to use a barrel approximately 38" long. Not exactly a practical length for a barrel, and since any barrel I've seen would have to be replaced to get that length, it would be easier to replace it with an 8" twist barrel of more normal length like 22" to 24" on a .243.

Bottom line: a 1" increase in twist can and does make "the" difference if a bullet is on the threshold at the slower twist which it is in the post that started this thread.

Fitch
 
Fitch, That book is a very good read. And you're right, physics is physics. But 105's do stabilize out of my 9 1/4 twist factory 243, they don't shoot as well as 95's, but they do stabilize. I know alot of guys in New Mexico using 105's in factory 700VLS's with great luck, but we are talking a 6000 ft elevation change from where we're at in Pa
 
Thanks Fitch. My experience tells me the same thing. The real issue here is not "recommended" twist, it is actually RPM. That is the true deciding factor, and the real way to figure out if a bullet will stabilize given a certain twist and velocity. Sometimes certain cartridges of a given caliber will stabilize a bullet with a slower than recommended twist rate. However, if most will not, manufacturers still have to recommend the faster rate of twist in order to accomodate the majority. Hope this makes sense.

JBP, will your 1-9.25 stabilize a 105gr VLD, though?
 
Originally Posted By: JBPrecisionFitch, That book is a very good read.

It sure is. I didn't know enough to know how much I didn't know about ballistics till I read it. IMO it is the best money I've ever spent on a book related to shooting, and I have a bunch of them.

Quote:And you're right, physics is physics. But 105's do stabilize out of my 9 1/4 twist factory 243, they don't shoot as well as 95's, but they do stabilize. I know alot of guys in New Mexico using 105's in factory 700VLS's with great luck, but we are talking a 6000 ft elevation change from where we're at in Pa

Yup, less dense air helps because it reduces the aerodynamic forces tending to destabilize the bullet.

Sometimes a rifle twist/bullet combination is right on the edge. My 9" twist LRPV .22-250 was like that. It used to shoot the Hornady 75g HPBT really well when loaded close to max - won the factory class GH match with it twice (the first two times I entered the rifle - match has relays at 200, 300, and 500 yards). It also shot the Sierra 69g SMK into similar sized groups but the heavier bullet was a tiny bit better in the breeze at 500 yards). Since I cut 1-1/2" off the barrel to set it back (the throat was shot out after 2,500 rounds or so) they don't tumble but it doesn't shoot them nearly as well as it did. It still shoots the 69g SMK into tiny groups like it used to. That same rifle never would shoot the 75g A-Max worth beans. The A-Max box says it needs 1:8" twist - they aren't kidding.
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Fitch
 
2MG, sorry I didn't specify. Yeah, I was talikng about the VLD's. It stabilizes them and they shoot well but the 95's shoot better.

Fitch, There are many good books out there that anyone who is serious about shooting should read that will explain every influencing factor that a bullet faces. I think that Brian's book does the best job at explaining them in terms that you do not need a wall full of degree's to understand. Well worth the $40 to anyone interested
 
I nteresting. You are the firast one I heard say that out of a lot of people. How fast ya runnin' 'em? We are talking in PA right. Not @ high altitude?
 
Yeah Pa. Was a couple years ago but I believe they were around 3050. I'd have to dig out my records on it. I've since punched it out to an AI and shoot the 95's. If I remember right it was 3050 with 49gr of Retumbo. Was a load John Burns uses, thought I'd give it a try. Shot under MOA out to 1000 but I just wasn't really happy with it
 
This post cracks me up. FWIW, I agree with toomuchgun. The Berger REQUIRES a 1-8 twist, much like the 70+gr bullets in 224 calibers do.

I, too, have accurately shot long Vmax bullets from my 223 caliber rifles, but Bergers are a whole nuther animal. It has NOTHING to do with what the bullet weighs, and EVERYTHING to do with bullet length and ogive design, thus the VLD (very low drag) or VERY aerodynamic, or very long.

That aside, IMHO, the crown would have to be destroyed to make a bullet tumble. A damaged crown will make for big groups, though.

Back to point of the original post, it matters NOT what one rifles does, and another does not. HIS rifle, even IF he has a 1-9 twist, is keyholing THOSE bullets, thus the bullets are NOT stable when leaving the muzzle.

The simpliest solution is to get another 95-100gr bullet of suitable design for HIS twist rate, and use them.

For kicks and grins he should measure the twist rate. The reason one might shoot a heavy bullet fine and another may nost is simple. Not all 1-9 twists are TRUE 1-9 twist. I have seen some that are stamped 1-9 and actually measure out at 1-8.25, and others that are stamped 1-9 that measure 1-9.5. It all depends on the accuracy of the machines they were made on.

I can guarantee you, the former barrel will stabilize a heavier/longer bullet than the latter one.

The OP's barrel, might measure out closer to the 9.5 than 9.0.
 
Originally Posted By: FitchOriginally Posted By: JBPrecisionFitch, That book is a very good read.

It sure is. I didn't know enough to know how much I didn't know about ballistics till I read it. IMO it is the best money I've ever spent on a book related to shooting, and I have a bunch of them.

Quote:And you're right, physics is physics. But 105's do stabilize out of my 9 1/4 twist factory 243, they don't shoot as well as 95's, but they do stabilize. I know alot of guys in New Mexico using 105's in factory 700VLS's with great luck, but we are talking a 6000 ft elevation change from where we're at in Pa

Yup, less dense air helps because it reduces the aerodynamic forces tending to destabilize the bullet.

Sometimes a rifle twist/bullet combination is right on the edge. My 9" twist LRPV .22-250 was like that. It used to shoot the Hornady 75g HPBT really well when loaded close to max - won the factory class GH match with it twice (the first two times I entered the rifle - match has relays at 200, 300, and 500 yards). It also shot the Sierra 69g SMK into similar sized groups but the heavier bullet was a tiny bit better in the breeze at 500 yards). Since I cut 1-1/2" off the barrel to set it back (the throat was shot out after 2,500 rounds or so) they don't tumble but it doesn't shoot them nearly as well as it did. It still shoots the 69g SMK into tiny groups like it used to. That same rifle never would shoot the 75g A-Max worth beans. The A-Max box says it needs 1:8" twist - they aren't kidding.
grin.gif


Fitch

To contrast this, I have 3 different rifles, all in 223 caliber, a Ruger Mini 14 Target, a Savage bolt, and a Savage LRPV. All are 1-9 twist, and all three will shoot them under an inch. I read the "1-8 required" as well, but it's not always the case. They were loaded long enough that it was a single shot proposition for the Mini though. As a matter of fact, those were the very first loads fired from that rifle.
 
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