Neck Tension

armednfree

New member
Working with the 68 grain Hornady Match bullet. The nose is both hollow and the jacket rather thin. To one degree or another it leaves a ring around the nose. It does this with a Hornady match seating die. Hornady just sent me a seating stem for an ELD that I'm going to try.

I know people are saying the ring doesn't make a difference. Probably not one that I could see, but I still don't like it. I already mitigated it somewhat by brushing the inside case neck and putting on a heavy chamfer.

The only thing left is to reduce the neck tension from .002 to .001, but will that hold in a magazine (AR-15) or will the bullets walk out? I used that tension in HB bolt rifles, 1000 yard stuff, but that was loaded single shot.
 
Did you chamfer the case mouth?
The ring doesn't matter(only the base of the bullet matters), but it's caused by the shape and diameter of the seating plug. Pointy match bullets are seated with a spitzer seating plug. That still might be too small for a Hornady Match bullet(been using 'em in .30 cal for eons). An RN seater might be a tick bigger.
Neck tension is not something you can adjust. Are you talking about crimp? You won't be adjusting that by 1 or 2 thou either, but match ammo out of a bolt action doesn't require a crimp. An AR might like a bit though. Only enough to hold the bullet in place under recoil and no more. It's one of the many reloading things that are defined as "enough".
 
Neck tension is adjusted by the diameter of the case mouth. Typically it will be .002-.003 less than bullet diameter but I've taken it down to .001.
 
Neck tension is adjusted by the diameter of the case mouth. Typically it will be .002-.003 less than bullet diameter but I've taken it down to .001.


In Bryan Litz's book Modern Advancements in Long Range Shooting Volume II he does and entire chapter on neck tension. For his .223 using Berger 80 gn and Benchmark the velocity only dropped 6 FPS from increasing neck tension from .001 to .003. The SD of the test rounds also dropped from 9 to 6. Just something to consider
 
If the rounds are to be used in an AR, I would stay with the .002 to .003 tension. I use that for the '06 Garand loads. The marks on the bullets you are referring to are of course made by the contour of the seating stem and could probably be eliminated with some polish buffering.
 
This isn't about neck tension, this is about a bullet seater that matches the ogive of the bullet, and how rough machine the bullet seater is.

Rings are most common on seater/crimper dies where the crimping process is trying to hold the bullet in place while the seater continues to push the bullet down into the case.

Seaters OFTEN have lousy machining that imprints the soft copper jacket, sometimes just a polish is required.

When I want an exact match to bullet ogive, I simply start with the seater that most closely matches the bullets I'm using, then I break out a drill motor & lapping compound, sacrifice a few bullets lapping the seater both smooth, and fitting the bullet profile MUCH better.

The idea that one size fits nothing dies are sacred and can't be touched is long lived and makes no sense.

Having an issue with seater dinging your bullet points, then break out a drill motor & drill, relieve the point pocket a little.
Leaving rings? Lap out the ridges & increase contact area with more of the bullet jacket so it doesn't leave rings.

Sizer die not bumping the shoulder back quite enough?
Shoulder winds up where you want it when you slip feeler gauges between shell holder & brass?
Simply lap a little off the bottom of the die or top of shell holder.

The dies are made to work EVERY brass in your caliber, NOT fit your specific chamber, or your specific bullet. Feel free to make them so!

Now, a shocker!
You CAN make a $25 die set fit your specific application when the high dollar ($150 & up) dies won't fit as well with a few simple changes!

The one that kills me most is how virtually EVERY combo sizing die crushes down brass necks WAY more than they need to be, then expands them back out.
This WAY overworks the brass at it's most crack prone point!

It's super simple to hone the neck out in a die to fit YOUR choice of brass.
Wooden dowel rod, sandpaper, lapping compound & drill motor.
A scrap brass you can cut the neck off and drill the primer hole out makes an alignment tool and protects the shoulder in the die.
It's that simple!

Expander ball not giving you a reasonable fit for your bullets, a piece of leather, lapping compound & drill motor, take a little off the ball to increase neck tension to find it your chosen bullets.
 
No I use .003 neck tension on my .260's and .308's whatever tension a Lee collet provides on .223 on my bolt gun and the AR fodder gets a trip through a RCBS FL X die. I even quit using neck lube because I found it did not help with anything. In post 4 I referenced how Bryan Litz dispelled the myth of low neck tension doing anything useful and if you want low SD's to use .002 or .003. But if you still want to use .001 and want to check bullet pushback do this.

load a dummy round ( no powder or primer) with a bullet using .001 neck tension. Measure COL or base to ogive. Place the bullet in the magazine and fire as many times as you want using normal ammo but do not let that bottom round get chambered. Pull the magazine and measure again to see if it was pushed back
 
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I got the ELD/AMAX seating stem. It still leave a ring on the bullet just farther down. Also the bullet tip does not bear against the inside of the stem.

I think some valve grinding compound and chuck a bullet in a drill and I might just be able to lap it into a better fit to the ogive.
 
Feeding from a semi auto is going to be iffy with very min neck tension.

The real trick of the game is to achieve uniform bullet pull forces which will lower your standard deviation and eliminate high and low shots at long range.

The amount of resistance you feel seating the bullet means nothing, the uniformity of bullet pull is critical for long range work.
 
Armednfree,

If you don't like the look of that ring mark, just imagine how upset you would be if you could see the bullet leaving the muzzle with all those gross rifling marks swaged into it! The ring has no effect on exterior ballistics for the same reason the rifling marks don't change the BC of the bullet; they are covered up by the boundary layer of air that travels with the bullet in flight. That layer is due to the fact air molecules are attracted to and actually stick to the bullet surface and try, less hard, to stick to the air passing by, and the two influences collude to attract a following of molecules a few thousandths of an inch thick that form the boundary layer. In a bullet, that layer is turbulent, and if you ever get to look up close at the shadowgraphs of flying test projectiles in the late Robert L. McCoy's book, Modern Exterior Ballistics, you will find you can see it quite clearly and even make out the turbulence in it. Thin, but there.

It is not true that only the base matters, but it matters more to group size because small errors in the base interact with muzzle blast to introduce drift away from the ideal trajectory path, thereby opening groups up. It takes a much bigger nose distortion to do that because the influence on the nose is from the headwind and not the brief tailwind of muzzle blast. The headwind is continuous, so whichever way it pushes the bullet is reversed every half rotation of the bullet, undoing much of the previous half turn's error. Thus, as Harold Vaughn showed, He could cut a 45° slant on the nose of a bullet and only open the group up by about a quarter of what a mere 2° slant on bullet base caused. Harry Pope famously remarked that "the base steers the bullet". Over a century later, that is still true. But it must be added that the nose is largely responsible for determining ballistic coefficient, with a perfectly pointed base having around a third of the effect on it that the same shape nose does (you can test this by firing bullets backward). Each end plays its role.

So, the ring is a purely cosmetic issue for unfired ammunition. In order to accept long bullet noses, the recess machined into the ramming end of the seating stem of your die has a steeper angle than the line tangent to your bullet's ogive where the two meet. If the mouth of the recess is left sharp, that edge both shaves and impresses the ring into the bullet.

As already mentioned, if you use one bullet all the time, you can sacrifice a couple of them as laps to alter the seating ram mouth with fine lapping compounds and polishes. It doesn't take much. A small fraction of an inch of matching profile will spread the load out enough to mostly eliminate the ring. If you want to try that and haven't ever done lapping before, I recommend drilling a few quarter-inch holes in some scrap steel and practicing. You want to work the lap back and forth and not turn it in just one direction if you plan to avoid making circumferential scratches on it. You want to turn the work a bit every few lapping strokes to average out the pressure angle of the lap, or else have the work rotating slowly as you do the lapping in order to get the most perfectly even job you can.

The simpler thing to try first is to chuck the seating stem in a drill and turn it slowly while you dull and polish the edge of the mouth of the ram. A Dremel tool and Craytex tips will do a fine job of that. Just progress through the grades of the tips from coarse to fine until that mouth edge is rounded and smooth. When you are done, the ram still contacts the bullet over a small area, but it is no longer sharp so the ring indentation has a gradual side slope and fresh subsurface copper is no longer being exposed. This leaves it much less pronounced.
 
Neck tension: Most of my life I have dealt with crush fit and interference fit; and then I got involved with reloading, in reloading there was nothing but tensions this and tensions that. No one had a tension gage and no one had a way of converting tensions to pounds. I have always though tensions was a way to talk about something a reloader knew nothing about.

And then one day a company that builds reloading equipment designed a seating tool that measured the effort necessary to seat a bullet. From the beginning I knew the tool would not be marked off in tensions from the beginning I knew the tool would measure effort in pounds with no conversion from pounds to tensions.

I have made a few tools that reduced the effort required to seat a bullet, for seating bullets I have used aluminum can crushers, bottle cappers and corkers. When seating bullets I have found the alignment between the neck and bullet made the biggest difference. I have no way of knowing how a reloader can turn that into reducing neck tension but for me it only shows up on a tool that measures effort in pounds.

F. Guffey
 
for F Guffy - what is the metric equivalent of the imperial unit of measurement that you call "tensions" ?

Neck tension: Most of my life I have dealt with crush fit and interference fit; and then I got involved with reloading, in reloading there was nothing but tensions this and tensions that. No one had a tension gage and no one had a way of converting tensions to pounds

I am the one that does not have a tension gage that measure tensions, I am the one with tension gages that are calibrated in pounds. And then there is annealing; tension and annealing can be talked to death.

F. Guffey
 
Hounddawg,

I think you found Mr. Guffey's point: The tension isn't normally what you measure or are even directly interested in. Bullet pull force is what you are after. But just for the sake of completeness, if you measure tensile stress (hoop stress in the case neck) caused by seating the bullet, the units will be psi in imperial units and bars or pascals in metric units.

You can calculate the pressure the neck puts on the bullet surface. It's just calculating backward from the hoop strain (the difference in neck circumference before and after seating the bullet) to find the hoop stress, and from that you find the pressure the neck places on the bullet, which is just equal to the internal pressure that would cause the same amount of hoop stress in the neck if it were caused by pressurized gas instead of a seated bullet. Again, it would be in psi or pascals or bars. From that and the amount of bullet surface area in contact with the neck, you arrive at the internal force of the neck. Multiply it by the coefficient of friction between the neck and bullet and you get the bullet pull force.

How accurate that would be, I don't know. The inside neck surface roughness and the presence of carbon and any inside neck lube you might have used in sizing will all affect that coefficient of friction. But it seems like one of those things that would vary enough from one case to the next that you would be way better off just measuring bullet seating force directly and assuming it will match bullet pull, at least when the cartridge is newly assembled. It will get higher as it ages, so you'd have to sample and pull bullets and measure that, too.

There is much bother in doing all of that.
 
Isn't this subject just a matter of disagreement on terminology? Everyone at least knows what bullet tension refers to whether it can be measured in lbs or lbs/Sq in. We can say that bullet tension or bullet release is so many lbs to release the bullet, but since we don't have a tool to commonly measure that, about the only thing we might best say is that bullet tension equates to .003" etc, as determined by the expander. The point being that most everyone accepts the terminology bullet tension whether that is the correct wording or not.
 
That was my point, 'Tension' is a measured value, not the diameter of the neck.

Tension has to be measured by a strain gauge or cycling dyno.
Neck diameter interference fit to bullet is simply a crude way to express the interference fit.

Since you are working with a 'Circle', and most will be working with crude measuring tools at best, it will be difficult to even determine an accurate diameter of case neck or bullet, and since surface area/volume changes so radically in a circle the interference can't be accurately determined.

And like Guffy noted, without taking into account the elasticity of the brass, there simply no way to account for that vairable.

Then there are vairables in surfaces, what slides on what easier...

Without a calibrated 'Pull' or 'Push' test machine (strain gauge) you can't even begin to know values.
Doesn't matter if that machine is imperial or metric, the MACHINE/recording equipment is needed.

What I've tried to tell folks in previous threads, I have access to a cycling dyno calibrated in 1/100 grams and can record 100 data points a second.
What I was trying to tell people is this doesn't work like you *Think* it does...
If 'πr2' isnt something you recognize, then don't chase this rabbit down the hole, you have zero chance of figuring this out.
 
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