Do I need to neck turn?

[AZShooter]

I have a 30 BR that is using .0105" neck wall thickness with .001" release per side.

I would say you could go even thinner but if you use a repeater recoil might move the bullet too easily as the thinner walls don't offer much neck tension.


Getting back to neck turning. I bumped into a great article on accurateshooter.com
where they discuss no turn vs turned necks. This is a BR site and naturally the article below is discussing BR equipment. So take it as it was intended. LR hunting certainly has different considerations such as having to work with more neck tension as most of us use repeaters:



Tunnel Tests Show Superiority of Turned Necks

Turning necks is widely, if not universally, done by short-range benchresters shooting 6 PPC and 22 PPC cartridges. On the other hand, many long-range shooters, using bigger cases with longer bullets, have had great success with sorted, but non-neck-turned Lapua brass. For example, Richard Schatz has set multiple world records, and won many major matches shooting his no-turn Dashers.

Turned necks still completely dominate the short-range benchrest game. But, do we have any hard evidence of how much of an advantage turned necks offer? And, is it fair to say that turning necks is less advantageous with longer, heavier bullets typically used for 600- and 1000-yard benchrest?

Lou Murdica is a very skilled benchrest shooter in California. This editor has personally seen Lou finish first in a short-range BR match competing against some of the best shooters on the West Coast. Lou does a lot of serious comparison testing of components, and he has access to an indoor tunnel. The tunnel allows Lou to eliminate (or at least minimize) wind effects when testing ammo. Over the past few months Lou has been testing turned vs. unturned necks, and he recently posted some interesting conclusions.



Lou writes: "I don't want to say that what some people have done is wrong for them, but I have been testing for nine months, shooting three to four times a week. I have found that there IS a difference between turned brass and unturned brass. Turned brass has shot better every single time in my tests. However, I have also come to the conclusion that if you shoot with very, very light neck tension it is hard to tell the difference between turned brass or unturned brass. If you shoot with any neck tension, though, turning does make a difference and you can get flyers with unturned brass.

The benefits of neck-turning showed up more in the 22 calibers than the 6mm. Moreover, I shot thick necks in the 6mm better than the 22. I found that the 22 wanted more release that the 6mm. I could get the 6mm to shoot tight necks easier than the 22.

For what it's worth, I think that everyone should at least clean up their brass with a turner. All these years people have tried to find short cuts in shooting benchrest and every time we always come back to the same steps and care in making brass as before. I think it's a given that if you want to compete at the top you cannot take short cuts. You may get by once or twice, but in the long run it will hurt you.

Since 1991 when I was on the winning team at the 1st World Shoot in France, I started to experiment and shoot every weird thing I could find or build. I tried more crap, bought and built more guns and while doing this I tried to shoot every shoot I could across the country. I took Tony Boyer's class three years back, and the first thing he told me was pick a couple of guns out of all of them and shoot 6 PPC and nothing else for the next couple years. He told me to spend my money on barrels for those guns. Well, I did as he suggested and boy, it made a difference in my shooting.

What I'm trying to say to all the guys that have been shooting benchrest for a while and are starting to travel to the bigger matches is, stick with proven goods that have dominated for years, like the 6 PPC, with turned necks. You can try the weird stuff in practice."

Neck-Turning, Neck Tension, and Longer Bullets
–Does a Different Rule Apply?
Keep in mind that Lou is primarily talking about short-range PPC loads with short, flat-base bullets. Those who are shooting beyond 400 yards typically use longer boat-tail, high-BC bullets. These have a smaller, less pronounced pressure ring, a much longer bearing surface, and weigh two to three times as much as a 6mm PPC match bullet. The longer bullets are also propelled by slower powders, operating in a somewhat lower pressure range than is common for a competitive 6 PPC load. Notably, top 600-yard shooters like Terry Brady and Richard Schatz have found that these long bullets prefer relatively light neck tension, meaning the neck is sized to just .001-.002 under a loaded round.

This takes us back to one of Lou Murdica's observations. Lou said: "I have also come to the conclusion that if you shoot with very, very light neck tension it is hard to tell the difference between turned brass or unturned brass." Though Lou was mostly working with the lighter bullets, perhaps his observations explain why unturned brass has worked surprisingly well with the heavier bullets with long bearing surfaces. Since those long bullets typically work best with relatively light tension, maybe the benefits of turning necks are not so great, and that's why someone like Richard Schatz can win with no-turn Dasher brass. Richard was the 2007 IBS 600-yard Shooter of the Year.

This is not to say that turned necks can't benefit the 600-yard shooter. Murdica also shoots 600 yards, and he believes neck-turning helps long-range accuracy. Don Nielson absolutely dominated the NBRSA 600-yard Nationals using brass that was carefully neck-turned with his Pumpkin neck turning tool. Don strongly believes that his turned necks helped with accuracy and shot-to-shot consistency. So the jury is still out on the merits of neck-turning with longer bullets in bigger cases, but we applaud Lou Murdica for doing some serious research and putting in the "tunnel time" to confirm the benefits of turned necks for the short-range PPC shooters.

 

[Bart B]

Many folks get 1/4 MOA accuracy at 100 yards, 1/3 at 300, 1/2 at 600 and 3/4 MOA at 1000 yards with unturned necks. As long as the neck wall thickness has less than a .001" spread, they're good to go.

Turning necks to a uniform thickness takes a 1/4 MOA (or better) at worst rifle and ammo to see the difference; plus someone who can consistantly shoot that stuff that well. Benchresters may well see a 1/16 to 1/8 MOA improvement shooting their super accurate rifles in free recoil. Folks shooting anything off their shoulder holding them with their hands as they rest atop something on a bench are hard pressed to see that much difference.

Neck walls can be 1/25th caliber (bore diameter) thick at a minimum. 30 caliber cases would then have a minimum neck wall thickness of .012". Some folks go thinner, but that may cause sizing problems with most dies unless you use one with bushings of the right size.

All in my opinion, naturally.

Fact: turning bottleneck case necks (on cases headspacing on their shoulder) to uniform diameters does not help center them in the chamber neck when they're fired. They float clear of the chamber neck wall by 1 up to a few thousandths. Those cases are centered in the chamber shoulder by their own shoulder. If the case neck's .001" off center on the case shoulder, it'll be off center in the chamber neck by the same amount.

 

[AZShooter]

IMO and the author in article above, is that turning the necks was all about consistency. When the neck wall thicknesses are all the same the result is similar neck tension and bullet release which aides in accuracy.

 

[Bart B]

IMO and the author in article above, is that turning the necks was all about consistency. When the neck wall thicknesses are all the same the result is similar neck tension and bullet release which aides in accuracy.

In the ammo industry, bullet release force is the term used to express how easy or hard it is to get the bullet out of the case. They use tools to measure how many pounds of force it takes to pull the bullet out. How tight the case neck grips the bullet as well as the friction between bullet and case determines the force needed to do so.

With a collet type bullet puller gripping the bullet and weight added to a bucket attached to a shell holder with the round in it, the amount of weight needed to pull the bullet out could be easily and very accurately measured. In my tests of turning necks from exact thickness all the way around to just enough to remove brass 1/2 to 3/4 the way around the neck and having no more than .001" spread in wall thickness, the release force average and spread did not significantly change. Nor was there any accuracy difference through 1000 yards

7.62 NATO match ammo has a release force spec of at least 40 pounds. My measurements of both M118 and M852 ammo showed an average force of around 50 pounds with a 20% spread. Yet that ammo would shoot under 1 MOA at 600 yards, under 1/3 MOA at 100 yards. Good commercial .308 Win. match ammo I've measured has release forces around 20 to 25 pounds with the same spread; it's shot 1/4 MOA at 100 and 2/3 MOA at 600 yards.

Sierra Bullets does no prep on cases used to test their bullets for accuracy. Nor do they work up loads for a new barrel or new lots of bullets, primers, cases and powder. Their best match bullets go into 1/4 MOA at 200 yards from such cases using these procedures.

All of which to me means, unless you can shoot your stuff into no more than 1/4 MOA at 100 yards, turning case necks to exact, or nearly so, thickness is a waste of time. There's other things that'll improve your ammo's accuracy that's a lot easier to do.

 

[AZShooter]

Thanks for those details Bart B.

I will continue to use no turn neck reamers for most of my barrels. I will still turn down my 30 BR's neck to fit that tight chamber or any brass that ends up more than .015" after necking down.

 

[Mikecr]

Bart, the problem with a 'bullet release force' measurement is that it does not actually represent 'bullet grip' , or tension. In fact, if not controlled, it might mean nothing at all.

I compare seating forces with an electronic loadcell, as I've yet to design/built an actual tool for grip force measure. I do so knowing that this is relative and a not real internal ballistic factor.
But since I control every aspect of it so well, it does work to meet it's intent for me.
That is, I can actually see a measure implying tighter gripping force on both my meter and chrono.

There are two valid neck tension paths related:
1. Lighter tension = lower tension variance = lower ES and better tune(with load A)
2. Heavier tension = consistent pressure peak = lower ES and better tune(with load B)
They conflict, and there are of course gains AND prices to pay elsewhere, with each(and everything).

Often PB BR shooters need both, so they turn necks thinner and jam seat to effectively accomplish both. This is purely part of reaching tune at competitive load levels, and in capacities way smaller than hunting capacity cartridges. A disadvantage is in loosing seating adjustment off the lands.
Reloaders for distant shooting are challenged with more abstracts, and there are no trends that hold in neck thickness. But, with this there are fewer constraints(it's wide open).

A big ole Weatherby shooter might get his system shooting pretty good for a big ole Weatherby, 1/8" off the lands and with necks 15thou thick, while breaking every rule in point blank BR.
That's fine, it's not a tiny little BR toy.

 

[Truc]

7mmSAUM, shooting necked down norma 300 SAUM brass
Reamer neck diameter 0.321
Loaded case neck diameter 0.316
Full lenght sized unloaded case 0.314
Fired case diameter 0.319
redding standard fell length sizer was the die I used

Reason I ask is I loaded up some ammo off of Berger reloading manual. used their 168 VLD to start with but was shooting 162 hornday match bullets so I figured it would be fine but was showing some pretty good amounts of pressure. fired 2 rounds and stopped there.

Load was 56 gr. of 4831sc at 3.060" OAL

My standard load w/ a 180 Berger is 58 gr of H-4831 59 starts to show some ejector marks. Two grains more for the 168 Berger loaded at 2.9" OAL right at the lands
Your OAL would be an extremely hard Jam in my rifle and would spike pressures with a lot less powder.
As far as turning necks, unless your reamer is a tight neck don't do it. You will work your brass too much and need annealing or will split. Since you are using Norma brass the neck consistancy is better than most others.
When accuracy is measured in .001" or less, everything you can do to make your rifle more accurate is worth it, but in hunting will 1/3" MOA make a difference? Maybe over 1500 yds. I shot the 6 Dasher in comp and that rifle w/ turned necks have shot numerous groups measuring under 2.2" with an agg of 2.82"
In short range I lost a match at the Super Shoot some yrs ago at 200 yds by .0001" yes 1/10,000" and the total for the day was .2482" agg, **** Jack Sutton of Hart Barrels

 

[Bart B]

Bart, the problem with a 'bullet release force' measurement is that it does not actually represent 'bullet grip' , or tension. In fact, if not controlled, it might mean nothing at all.

Mike, I'm thinking static rather than dynamic conditions. And I'm also referring to the force needed to push the bullet out of the case when it's fired, not the force needed to seat the bullet in the case measured with with any electronic or mechanical tool as you mention. To say nothing of the surface characteristics of the case mouth and bullet jacket which will cause more or less resistance to moving the bullet for a given compression force (neck tension?) the neck walls put on the bullet. Nor is the issue with cases with unturned necks with thicker neck walls at the shoulder and thinner ones at the mouth which is often the way things are. Besides, the ammo making industry typically uses "release force" as the physical stuff needed and it's what most folks easily relate to and can easily measure themselves with inexpensive tools.

Info from another forum on this subject.......

A fellow who had participated in the HP White tests in the 1970's said they'd found bullets didn't start moving until about 10,000 psi. QuickLOAD thinks it's more like 3600 psi. Force on the bullet's equal to pressure in psi times cross sectional area of the bullet. Pressure increase partly stalls as the volume expands as the bullet slips from case neck to throat. There's at least one plot in the 1965 Lloyd Brownell study (link below) showing pressure flats at around 12,000 psi. So this can vary.

http://deepblue.lib.umich.edu/bitstream/handle/2027.42/3866/bac6873.0001.001.pdf

In the dynamic system, even though bullet pull is only 60 lbs slipping from the neck under the kinetic friction coefficient, given the short length of time the bullet has to start moving, its inertial resistance is a significant addition to that. The result is that instead of graciously popping forward, the neck is actually expanded from the rear by pressure, rolling forward almost to the case mouth before the bullet is fully released. This is the reason the mouths of fired cases are usually curled inward a little bit as compared to the rest of the neck. The rest of the neck expanded, but as the expansion neared the mouth, gas started leaking past it and equalizing pressure on the other side, so the mouth ceased expanding. We know this begins before the bullet has obturated the bore because super high speed photos show gas and powder particles preceding the bullet at the muzzle. Dr. Brownell attributed the effect of seating distance off the throat to the amount of greater gas bypass the deeper seating allowed.

Once you get to the rifling, Harold Vaughn showed 6mm (or .270) need around 1200 lbs of force to swage them into the rifling. That was about 20,000 psi static pressure equivalent, but assuming the kinetic coefficient of friction is about half the static coefficient of friction, about 10,000 psi would be right under dynamic conditions and with the bullet already moving.

 

[Mikecr]

I'm pretty sure the neck has completely released before there is any bullet movement, and that 'pull force' means nothing really.

-Take 10 cases with same neck tension, and polish/alcohol wash neck IDs on 5. Load all the same, uncoated/cleaned bullets, & shoot across a chrono. You will see no difference.
This, even though seating/pull forces are significantly different with the squeaky clean necks, and challenging our ability to seat bullets equally with uncleaned necks.
-Now test 10 cases with 5 partial neck sized 1/4 length, and 5 partial sized 3/4 length. This is where you will see a difference across a chronograph.

It is simple grip force that affects bullet release, and not friction.
Yes, there is blow by, before the bullet even moves, AND before the necks have opened fully to seal.

 

[Bart B]

Mike, please explain how case necks enlarge diameter off bullets without moving the bullet with all that pressure on the back of the bullet. Does the neck start getting larger than bullet diameter starting at the mouth, or at the neck-shoulder junction?

How any bullet could remain in place after 99% of the case neck's expanded off of it and only a tiny smidgen of mouth area holds the bullet in place before all bullet-neck contact is gone and the bullet then moves. . . .

 

[Mikecr]

Expand the neck .000001 and the bullet is completely free and gasses are passing it. Not much pressure needed to do that, which I imagine builds at the nearest bullet neck junction and moving forward around the bullet.
Until then, a bullet rests with it's mass gripped by that neck, and isn't going anywhere fast.

 

[TracySes23]

Expand the neck .000001 and the bullet is completely free and gasses are passing it. Not much pressure needed to do that, which I imagine builds at the nearest bullet neck junction and moving forward around the bullet.
Until then, a bullet rests with it's mass gripped by that neck, and isn't going anywhere fast.

I'm assuming you're referring to a dimension of one millionth of an inch (.000001").
If that's what you meant, no one can mechanically measure a dimension that small. Even precision gauge blocks aren't held to a tolerance that small.

 

[Bart B]

Expand the neck .000001 and the bullet is completely free and gasses are passing it.

What about bullet and case surfaces with a 6 microinch finish? The case neck will have to expand more than 1 microinch to ensure all the micro-mountain tops clear those other ones on each surface. Meanwhile, some micro-mountain tops are down in micro-valleys and friction will be at hand when they move against each other.

No case neck insides nor bullet jacket has surface smoothness that small.

C'mon Mike. That's rediculous.

 

[TracySes23]

What about bullet and case surfaces with a 6 microinch finish? The case neck will have to expand more than 1 microinch to ensure all the micro-mountain tops clear those other ones on each surface. Meanwhile, some micro-mountain tops are down in micro-valleys and friction will be at hand when they move against each other.

No case neck insides nor bullet jacket has surface smoothness that small.

C'mon Mike. That's rediculous.

You're completely correct. Not only that, but the diameter of a bullet isn't held to that tolerance.