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Old 02-28-2020, 10:24 PM
elalto elalto is offline
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Default HELP with lead-free bullet problem

Hi All,

I have a Remington 722 in 6X47 that has been my "go to" Coyote rifle since 1968. The rifle is a 1/12 twist and has shot the Sierra 60grn HP (#1500) so well that I have never tried anything else.

PROBLEM = Kalifornia. I now must use lead free bullets in this commie State! The shortest 6mm lead free bullet I have found is the Nosler BT at 55 grains, however, it tumbles out of my barrel. I know what the reason is: the bullet is too long for the twist.

I have put a few in the lathe and shortened them BUT I have some questions which I hope one of you well experienced gentlemen can answer.

1. Is it the overall length of the bullet or the length of the bearing surface that is incompatible with my twist rate?

2. By cutting off the tip of the bullet I am left with a rather large "HP" how will this affect the bullet flight?

Thanks in advance for any and all help I can get.
Marcos (elalto)

Last edited by elalto; 03-03-2020 at 07:47 PM.
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  #2  
Old 02-29-2020, 12:59 AM
Bill K Bill K is offline
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I can not tell you for sure, but from what I read it is the bearing surface that makes or breaks what lead free bullet will work with a given twist. Believe you will find you are going to have to obtain a faster twist so the longer bearing surface will stabilize in your 6mm. I would check with a tech dept at Hornady, Nosler or Berger to get advice on best twist. Bill K
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Old 02-29-2020, 03:09 PM
Johnly Johnly is offline
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I can shoot 75gr. Vmax bullets out of my 1/14 6mm BR and have them stabilize at 3100 fps, so I'm surprised that you're having stability issues with a 1/12 twist barrel with the lead free 55 gr. bullets.
Are you sure the barrel is a 1/12 twist?
What is the bullet length of the Nosler lead free bullet?

John
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Old 02-29-2020, 03:47 PM
Jordan Jordan is offline
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I don't think it is bearing surface that is determinant, but over all length.
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Old 02-29-2020, 04:05 PM
Bayou City Boy Bayou City Boy is offline
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Quote:
Originally Posted by Jordan View Post
I don't think it is bearing surface that is determinant, but over all length.
Yupper........... I couldn't agree more. The bearing surface stuff is silly but it has circled the internet several times for quite a few years.

This has been an age-old internet debate issue, but empirically the bearing surface of a bullet has less to do with inherent bullet stability than it does to directly affect pressures generated upon the bullet being fired. Bullet stability is more a result of the combination of the factors of sectional density, center of gravity of the bullet, overall bullet length, base style, etc., which all go into the calculations for determining Ballistic Coefficient

The more practical real concerns with respect to bearing surface are that it impacts pressure, and the fact that you need to match bearing surface to an appropriate throat length to maximize usable case capacity.

The parts of the bullet furthest from its center of gravity have the greatest impact on the bullet’s stability. To get it truly and precisely right, you need to take into account the entire geometry/shape of the bullet. But... you can get a surprisingly good approximation of stability using only the overall length as a substitute for the complete geometry. This is what the Miller Rule for determining bullet stability does. It should be noted that there is empirical data that shows that it – the Miller Rule - is slightly less precise in determining an accurate barrel twist with flat base bullets than for other bullet base designs. An accurate barrel twist is nothing but a barrel twist that is more precise than 1 in 12”, for example. When all data for a certain bullet is entered into the Miller Rule math equations, the actual barrel twist rate might be shown to be 1 in 12.35” or maybe 1 in 11.85” as examples.

I ran across this fairly simple but observable empirical data a couple of years ago which correlates bullet stability and barrel twist rate to bullet length. Quoted below…………

“In my limited experience with this I found that bearing surface length of a bullet had a minor effect on stability compared to bullet length. My 2 encounters with this was when I purchased a box of 53 gr Hornady V-max bullets for my 22/250. Loaded some up and seen right off, on paper, that the groups were bad and bullet holes were oval. Done some research and found out that the 1/14 twist would not do the job. I decided to try something. The original length of the bullet was .830. By removing the plastic tip, the bullet then became .700. I loaded these up to try and shot .75 moa with nice round holes. The next case was a friend purchased a box of 168 Barnes LRX 7mm bullets. They would not stabilize in his 7mm Rem Mag. He asked me if I wanted them to try. Remembering what I had done with the 53 gr V-max I said yes. First, I tried them untouched in my 7mm/08 and they were all over the target and the bullet holes looked more like slots than holes. The original length of the 168 LRX was 1.587. With the tips removed the length became 1.422. Just removing the tips gave me groups of .650 at 100 yds and the holes were just that, nice round holes. In both cases the bearing surface remained the same only the length was changed. Nothing else. Just what happened to me.”

I know that this does not put the question to bed in many minds, but empirical data is of far greater importance in advancing an argument than is the old, “it only makes sense approach” which some bullet bearing surface folks try to use to “prove” that bullet bearing surface is the determining factor. It’s kind of like the old, “In God we trust. All others bring data” approach.

As added empirical data, notice that the Berger calculator uses overall bullet length for the Miller Rule math, but it does not consider bearing surface length. In addition, core material, whether lead, non-lead, or solid core are not a variable factor that needs to be considered. The calculator also asks for bullet weight (mass) which is used to determine that bullet’s moment of inertia which is saying roughly how fast the bullet needs to travel for it to stabilize. By using the bullet’s mass, the “skid factor” which is what moment of inertia is all about is part of the math used to refine a required barrel twist rate. Moment of inertia is a part of Miller’s calculations.

https://bergerbullets.com/twist-rate-calculator/

The only empirical data that has been shown to be factual concerning bullet core material is that lead core bullets are generally heavier than non-lead or solid copper core bullets of the same length. As a result, to obtain a certain bullet weight, such as 55 grains for example, the bullet length of a non-lead bullet needs to be increased in comparison to an equal weight lead core bullet. With the bullet length increase comes a need for an even tighter barrel twist rate to stabilize a non-lead bullet. Berger’s calculator takes this into account by requesting the total bullet length for any give bullet, whether its lead core or not.

We tend to over-think all of this. Once you find a bullet that your rifle likes, it typically means that the bullet length matches the required barrel twist rate for stability. After that, it’s all about shot placement. Shot placement has always been and always will be the most important factor in making a humane kill with any bullet, whatever its core material might be.

As an interesting aside, there is some empirical data which suggest that non-lead bullets will penetrate flesh and bone better than a lead core bullet will. I haven’t seen any solid reasoning yet put forth by anyone to explain why, but the demonstrating data does exist. Some are believing that it has to do with the deformation rate of one core type (non-lead) versus the other type (lead core).

YMMV………………

-BCB
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Last edited by Bayou City Boy; 02-29-2020 at 04:22 PM.
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Old 02-29-2020, 04:40 PM
Bill K Bill K is offline
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I respectfully disagree. The bearing surface is what makes contact with the lands/grooves and the twist of those barrels. This is what effects the rotation and stabilization of the bullet, not the length. Experiment with some and you will find see what effects your stabilization and grouping. Bill K
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Old 02-29-2020, 05:29 PM
Bayou City Boy Bayou City Boy is offline
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Quote:
Originally Posted by bill k View Post
i respectfully disagree. The bearing surface is what makes contact with the lands/grooves and the twist of those barrels. This is what effects the rotation and stabilization of the bullet, not the length. Experiment with some and you will find see what effects your stabilization and grouping. Bill k [IMG]file:///C:/Users/tac20/AppData/Local/Temp/msohtmlclip1/01/clip_image001.gif[/IMG]
OK......................

With all due respect, Bill, you are confusing Internal Ballistics where bearing surface is included, with External Ballistics where bullet length is involved. They are two totally different but related concepts.

Common definitions:

Internal ballistics is the study of the propulsion of a projectile. In guns, it covers the time from the propellant's ignition until the projectile exits the gun barrel.


External Ballistics deals with the behaviour of the bullet after it exits the barrel and before it reaches the target.


The bearing surface allows a bullet to have spin imparted to it while in the barrel. The spin rate is determined by barrel twist rate and not by bearing surface length. Bearing surface length does affect how much pressure is exerted behind the bullet while it is in the barrel due to a varying coefficients of friction on the bullet based on varying bearing surface lengths

The length of the bullet (a modified cylinder) determines whether the spin imparted on the bullet while it is in the rifle barrel will allow it to fly in a stable manner once it exits the barrel. If the bullet (once again, a modified cylinder) is too long for the spin rate, the bullet will tend to tumble in flight.

-BCB
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Yo no creo en santos que orinan.

Women and cats will do as they please. Men and dogs should relax and just get used to the idea.

Going keyboard postal over something that you read on the internet is like seeing a pile of dog crap on the sidewalk and choosing to step in it rather than stepping around it.

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Last edited by Bayou City Boy; 02-29-2020 at 07:06 PM.
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  #8  
Old 02-29-2020, 05:38 PM
Herb in Pa Herb in Pa is offline
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My experience with the lead free is limited to a 1 in 16 twist 22 Hornet. 30 grain varmint grenades are extremely accurate while the 36 grain varmint grenades will keyhole @ 100 yards. The 36's will stabilize in any twist faster than a 1 in 16.
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  #9  
Old 03-01-2020, 12:37 AM
elalto elalto is offline
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Thank you all for your responses!

BCB, I think you are right on and I tend to believe that the bearing surface length has little to do with bullet stability.

I have decided to experiment with the 55grn bullets that I have (Nosler BT). I shortened some today and loaded them up exactly as I do the 60grn lead core Sierra HP bullets that shoot so well in my rifle. I cut the bullets in my mill so that they are exactly .7320" (as the Sierra's) from the original .950" (of the Nosler's).



The only question I have now is that after cutting the tip off the bullet I have a large "hollow point" what do you all think this may do to bullet flight and the poor coyote at the receiving end??



Thank you all,
Marcos (elalto)

Last edited by elalto; 03-01-2020 at 02:37 AM.
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  #10  
Old 03-01-2020, 02:10 AM
Bill K Bill K is offline
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Just for drill Marcos, call Sierra tech and asked them what twist you should use or need to stabilize those bullets. Bill K ( I will say no more on this subject and post.)
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