Need help understanding Neck Tension

[ghh3rd]

I keep hearing about neck tension, and how important it is toward consistent accuracy. How does one control neck tension? Although I've been loading for about two years, I still basically clean my brass, then resize using the same die each time, resize the boolits the same way each time, etc.

I can tell it's an important component of reloading, but can't seem to glean enough information about it from posts - can anyone elaborate on how you can check for correct neck tension, and adjust it if necessary?

Thanks - Randy

[PAT303]

I'm having Buckshot make me some M die mandrels for all my cartridges and have bought crimp dies and Lee collet neck sizing dies for each to get some consistancy in my rounds. Pat

[Larry Gibson]

You can use bushing dies with the appropriate size bushing to size the necks just enough (my foavorite technique).

You can use an appropriate size M- die or expander to size the inside of the case neck to the appropriate size.

You can lap out the sizer to just size the cases enough.

Probably a couple more but those are the most common ways.

Larry Gibson

[btroj]

Neck tension is controlled by the final internal diameter of the neck of the case before seating a bullet. It , combined with bullet diameter, determine the neck tension. The other factor that needs to be addressed in some cases is the temper of the neck. Freshly annealed cases will have less spring to them and will give lower neck tension. Cases that have been thru many size/ fire cycles will have more spring which can affect neck tension.
Don't over think this. The key thing is to match the bullet diameter to the final internal neck diameter. In a revolver a top big expander can lead to low bullet pull which can not be overcome with a crimp. This is largely a problem with heavy charges of slow burning powder. A revolver has a throat of about bullet diameter so the bullet pull needs to be enough to ensure a good burn of the powder. If the bullet moves too much before a good burn starts you can get a squib, or bad accuracy at a minimum. A rifle is less of a concern as the bullet will quickly enter the rifling which will develop the pressure required. This is somewhat the same reason a light charge of slow burning powder is a bad idea in any cartridge.
I am sure 44 man will have more to say regarding revolvers and Felix can speak to neck tension in a bench rest application.

[RU shooter]

can anyone elaborate on how you can check for correct neck tension, and adjust it if necessary?

Thanks - Randy
Checking neck tension is as easy as measuring the case neck ID with a caliper and comparing it to the size of your bullet. I like .001-002 under the sized bullet dia. in my rifle use. ie: .311 bullet, neck ID should be .309-.310 it works for me.To control the amount I size the neck I use a Lee collet sizer and adjust the amount by screwing the die up or down very slight amounts and check the neck ID. With a traditional NS die this would be taken care of with the proper sized expander ball but as others have said you get some spring depending on how hard the necks have become and a .310 expander may still get you .309 or less neck ID. IMO the collet sizer is more flexible in this regard .

Tim

[prs]

I t hink it helps to understand just why neck tension, or lack there of, is such a common problem with boolits. Lead is a pizz poor internal sizer. The brass case ends up forming the lead instead of gripping it. This problem is fostered by the use of commonly available die sets which were engineered properly for harder copper jacketed bullets. The softer your choice of lead boolit, the less difference in internal case size and external boolit size can be effectively employed. The thicker and harder and stronger your case is, the less difference in those diameters you can effectivelly employ.

Like already posted, greater boolit or boolit retention in the case improves the very early stages of ignition of the powder. You get more consistent ignition and more efficient power from your charge. Very poor retention might even give dangerous hang fires where the bullet or boolit becomes an obstruction.

How to neasure boolit retention strength is good question. Froup size is always a good parameter. I purchased a Hornady bullet puller and was gonna devise a spring scale onto my press lever to measure pull resistanace, but my pull resistance was well beyond the Hornady puller's grip. It just ripped through my boolits without pulling them at all! I then tried to develop a "standard whack" with my impact/inertia puller and did notice that boolits loaded with good technique were way harder to pull than boolits loaded with lesser attention to detail.

So what are the techniques? For consistency, I recommend annealing cases about every three uses. Use a fairly hard alloy if possible. External size minimally and internal size to get only a small difference; just how small is going to vary by application and alloy and............ If your application calls for a crimp, then take it easy. I think the notion that better (consistent and stronger) retention is possible with a firmer crimp is BS. Firm crimp can distort the boolit and make retention less. I've heard tell of folks gluing boolits or bullets in cases, but I have not resorted to that - unless seating boolits with still tacky tumble lube and letting them cure before firing counts.

prs

[canyon-ghost]

The easy version, and not quite as accurate probably, would be to buy brand new brass, size, chamfer, expand and fireform in lots large enough to promote some consistency, say 500 or 1000 rounds at a time. After fireforming, neck size only.

And then, a good taper crimp is just a light one. Agreed, prs said it best there. A light taper crimp can accomplish just as much as a strong roll crimp (unless you carry ammo around in the truck or saddle bags). Or, use a levergun, lol .

This would all depend on your particular situation. I need to load at least 40 rounds at a time for silhouette shooting. I'm not sure I have time to turn necks or worry too much about it. That yet remains to be seen.

Ron

[Bass Ackward]

I keep hearing about neck tension, and how important it is toward consistent accuracy. How does one control neck tension? Thanks - Randy


If you are talking "consistent" ignition, then you talk a package deal of which case neck tension is only one part and then it is relative to case volume.

While some people believe in it exclusively, you must understand that consistent ignition is best obtained with a case that is filled with lead and powder. To do that you have the slowest powder that

The less ideal that this situation exists and the larger the case capacity you have, the more important it is. Problem is that brass is only so strong and it changes from case to case, you eventually reach a capacity where it has minimal effect and you are eventually forced to go to a faster powder that sort of compensates.

So the best situation is to control case capacity with a heavier bullet and or deeper seating of lighter slugs assuming you don't negatively affect feeding. (or headspace for automatic cartridges)

Both of these things provide more bearing area for the case to grip and still fill that case volume which minimizes the importance of "perfect" case to case tension. And it depends on clean necks, changing anneal, dies, how wide your grease groove(s) are, and how slick your slug is from lube.

Essentially, perfect or even close to it neck tension is a fleeting goal to obtain and you will compensate with powder speed / selection.

[montana_charlie]

I keep hearing about neck tension, and how important it is toward consistent accuracy.
The way in which it provides consistency is in how it regulates muzzle velocity from shot to shot.

You determine the 'amount' of neck tension by sizing the case mouth to a particular dimension below the diameter of your bullet. But the softness of the brass has an effect, too.

A 'hard' case sized for (say) one thousandth of neck tension will grip the bullet as hard as a soft case set for (maybe) two thousandths.

If you start with a new case, then load and fire it once a day using the same reloading tool...the unchanged 'neck tension' at the end of the month will have a much stronger grip on the bullet.
If you also crimp your loads, then it gets even more complicated...

The point is, if you are going to worry about it at all, you need to consider everything involved...case cleanliness, brass hardness/softness, crimp and crimp style...not just the dimension of your die or expander.

CM

[243winxb]

Measure the neck area of sized and expanded brass. On bullet seating, the neck must expand by as little as .0015" for a single shot rifle. Heavy recoil firearms need the case to expand on seating as much as .004" An expander .002" under bullet diameter is common. A military 5.56mm round has a bullet pull weight of 35lbs min to 45lbs. A case neck that has expanded .002" on bullet seating will give you this amount of bullet pull. [smilie=s:

[Doc Highwall]

The only thing I can add is why a Lyman M-Die is better then just a case mouth flair is that it expands the I.D. of the case neck for the whole length making all the cases closer to one another while putting a slightly larger step for the bullet to start.

[btroj]

I also think neck tension is more an issue in specific situations than it is in general.
For plinking type loads I don't worry about it. I also worry little about it in general use handgun loads.
For heavy loads in a handgun it is much more of an issue. I also would worry more in a target rifle application. In these situations it seems from my experience to make a much larger difference.
It is one of many factors that can play a roll in accuracy. Is it the most critical? Most likely not. Can it be ignored for best accuracy? No, but it needs to be looked at in relationship to Manu other factors such as bullet hardness, case neck to chamber fit, powder choice, and many other factors. Accuracy is never an accident. It usually takes a bit of work to find what will work best in your gun using the components you choose.

[Von Gruff]

I have opened up die necks, have M dies and bushing neck dies for various of my rifles and dies. I anneal at intervals dictated by the load intensity, that is more often for higher intensity loads than plinkers. but generally aim for 1-2 thou grip. Suficient to hold against chambering from the magazine and leave all the little inconsistencies of work hardening increments for the j words. I dont BR my cast boolits so any small changes between annealings are irrelevant as far as my end needs are concerned.

Von Gruff.

[btroj]

Yes Von Gruff, match your loading technique to your needs. That is the most simple you can make it.

[44man]

The rifle and single shot pistol is different then a revolver. You can change a lot in a rifle and anneal when needed but never anneal revolver brass. New revolver brass is worse then brass fired many times because tension is too different from case to case.
Tension in a revolver does not need to be extremely tight but needs to be more even from case to case and the best way is to just make all rounds tight. This means soft lead can be sized when seated so I use at the least, water dropped WW metal. I want the boolit to open the brass when seating, not the reverse. I have a system to measure seating pressure yet hardly ever use it because proper dies makes things even enough.
You can tell if you have a problem when you load if one boolit goes in real easy and another is real tight. These will not shoot to the same POI.
Crimp on revolver loads only needs to be enough to prevent boolit movement with all rounds in the cylinder.
Rifles can be shot with hardly no tension and no crimp. Many rifles are shot with hand seated boolits. Rifles with tube magazines or heavy recoiling rifles need tension and crimps but single shots are again different. This can be worked out by testing but the revolver is different in that some things can not be gotten away with.
Some say revolver dies are made for jacketed but this is not 100% true. Older revolver dies had large expanders for soft lead and did not work good for jacketed either. If you have an expander for jacketed, the solution is to make the cast act like a jacketed, make the boolit hard enough to seat without being sized. That will be proper case tension. The hard part is making them all even.

[fecmech]

I remember reading an article from a well known cast bench rest shooter who used 0 neck tension. When he initially set up his new brass after chambering his rifle he turned the outside of his case neck down a few thousandths(don't remember how much now) back to where he wanted the base of the bullet to seat leaving a slight step. After one firing that put the step on the inside of the brass and acted as a stop for the bullet. He fired each group with the single piece of brass by simply depriming, recharging the case with powder and seating the bullet in the case with his fingers. I wish I still had the article, I lost it a while back when my computer hard drive failed. He said the only way to get perfectly consistent neck tension was to have none! Obviously this only works in the bench rest type setting.

[felix]

Correct! The next step for improvement is to breach seat and use the same case for powder only. The final step would be to eliminate the case entirely and have the chamber itself be the powder seat, as in the naval guns. The 16 inchers have been computerized to hit a football field at 26 miles, which is 1.5 inch equivalent at a hunnert. ... felix

[montana_charlie]

He said the only way to get perfectly consistent neck tension was to have none! Obviously this only works in the bench rest type setting.
Many of us who shoot BPCR use it.
My paper patched bullets just slip into the unsized case mouth, and my grease grooved bullets are actually held in by 'lube suction'.



The final step would be to eliminate the case entirely and have the chamber itself be the powder seat, as in the naval guns.
...and the old percussion-fired Sharps rifles.

CM

[btroj]

Like I said, adjust the tension to fit the needs of your needs. Obviously no tension won't work in a repeater or a revolver.
This is why it can't be looked at as the only factor to address in accuracy. I always prefer to think forest, not trees.

[HangFireW8]

I keep hearing about neck tension, and how important it is toward consistent accuracy. How does one control neck tension? Although I've been loading for about two years, I still basically clean my brass, then resize using the same die each time, resize the boolits the same way each time, etc.

I can tell it's an important component of reloading, but can't seem to glean enough information about it from posts - can anyone elaborate on how you can check for correct neck tension, and adjust it if necessary?

Thanks - Randy


I hesitate to post this, because of the cost issue, but this is they way I see it. I went round and round on this with accuracy J-words, and finally came to this conclusion. There are two ways to do it:

1. Use standard dies (neck, full length, it makes NO difference, since they size the neck the same, just not the shoulder), and use custom expander buttons in various sizes. The result- short brass life, extra effort, an inventory of various expander buttons in .001" increments.

2. Use custom sizers for each neck tension need. In my case that means Redding "S" or Competition dies, and a set of sizer bushings in .001" increments. Other approaches are lapped-out commercial dies or custom cut dies.

http://castboolits.gunloads.com/picture.php?albumid=473&pictureid=3155

The result- my sized .30 caliber brass for .310" bores glide past the expander ball without effort, meaning the absolute minimal stress on the neck, no annealing, long brass life, and perfect neck tension.

I've been around the block on case annealing, and now see it only as a necessary evil for wildcat case forming. I don't care if you have one of those automated annealing systems, you will not get a batch of brass with consistent neck pull after annealing.

The ultimate goal is as low as bullet pull as is practical for the system (alas, fairly high for revolver). The reason? Let's say you can control bullet pull via neck tension within 10%, well 10% of 7 pounds is a lot less variance (and stringing) than 10% of 70 lbs.

[Doc Highwall]

I use the Redding bushing dies also and I have not turned my case necks which means that any case neck thickness inconsistency is now on the inside making another variable to bullet tension. This I believe is eliminated by using a M-die or Lee's collet die. If you check Sinclair Internationals catalog they now have a neck expander for bench-rest shooters who do turn their case necks to help with consistent neck tension. I size my case necks and check the I.D. with a set of pin gages so that a .309" pin will not enter and then use a .309" expander with a .3119" step to allow the gas check to enter the case as shown in my post above. My sized bullet diameter is .310".

[geargnasher]

I'm in the "forest" class usually, not the aforementioned "tree" class. For rifles, I have one sizing die for each gun, the neck portion honed to the size I need to achieve:

1. .0015" to .0008" total loaded case neck clearance.
2. .0015" neck tension on sized boolit.
3. The case neck thickness is the variable here, so I turn them to the necessary thickness to achieve 1 and 2.

Example: Rifle has .308" groove diameter, shoots .309" boolits best, likes .002" neck tension. Chamber neck is .336" DIRTY. Sizer die is honed to size case necks to .333" OD (actual size is .332" to account for springback), expander is .307" and is really just a springback checker in this example. Case necks are turned to .013" thickness which gives .001" total loaded chamber neck clearance. (.309+.013+.013+.001=.336). Before seating the boolit, the case neck OD is .333" and ID is .307", thus giving the .002" tension when the boolit is seated.

The biggest problem I've had when doing this is finding brass with thick enough necks. Production guns generally have fairly sloppy chamber neck clearances so they will function freely, but this isn't the most ideal situation for accuracy. Some of my rifles like groove-sized boolits, too, and that exacerbates the issue.

Gear

[44man]

Back when I did a lot of rifle shooting I was getting a lot of run out. I found it was not from seating a bullet but from the brass being sized too much and the expander being forced out even with lube, was doing the dirty deed. Weatherby brass bends easiest.
This was before the Redding collar dies so I would send fired cases and the size die back and have them lapped for minimum sizing. Back then the die makers did it free.
Even the .300 Weatherby was turned into a tack driver.
The Redding dies are the best thing ever!

[HangFireW8]

I use the Redding bushing dies also and I have not turned my case necks which means that any case neck thickness inconsistency is now on the inside making another variable to bullet tension. This I believe is eliminated by using a M-die or Lee's collet die. If you check Sinclair Internationals catalog they now have a neck expander for bench-rest shooters who do turn their case necks to help with consistent neck tension.

You make some good points, Doc. Neck tension still needs to be further managed, even if one uses bushing size dies. And, Sinclair will always offer an expensive solution to a simple problem, usually oriented towards j-word users who cannot make their own tools.

On my Redding die sets, I have swapped my expanding ball from the standard sizing die into my "S" or Competition die. This allows me to notice by feel when a tight neck (extra thick and/or extra soft brass) comes through. When I feel one like that, I set that one aside. It will not rejoin that batch, unless I can figure out a reasonable reason why (fired in a different chamber, for example), and correct it. (Sometimes I'll assemble enough of these to make a different batch, which means, it was probably a different batch to start with, just sharing the same headstamp in common.)

I then pre-check neck tension with a custom pin gauge .001 or .002" under what I am loading. I make these pin gauges from molten lead alloy and a mold, with a little copper cup pressed onto it and custom sized, using a special press made for that purpose. It may sound exotic, but most cast boolit shooters may find they already have this equipment if they look around. :) In some cases, you can buy these pin gauges in boxes of 50 or 100, pre-wrapped in copper and sized to match your bore. :)

So, if you have an undersized boolit sizing die laying around, you may now have a use for it. You can use it to make custom pin gauges for checking neck sizing.

-HF

[shotman]

one thing you cannot keep the exact tention useing the neck as sole unit. The crimp is what is going to make the difference. New brass, once fired , fired 10 times. different brands
There is no way to get same neck tention by one die. You have to use the crimp to control it

[Willbird]

Well I for one do not understand how the LEE collet dia can consistently produce different dia on demand ? As I understand it the die uses a collet to close the case neck against a mandrel...

Changing the mandrel size would change the inside neck dia...but backing the die off so the collet no longer closes the neck against the mandrel would seem to defeat the purpose of the die ?

To use the redding system of bushings it might be best to turn the necks to all the same thickness first. The bushings DO allow you to tailor the amount of sizing however, I checked several 22-250 dies once and they were closing the neck down .008 and opening it back up .006...that is a LOT of sizing...using a bushing die would allow closing down .003 then opening up .002 with the expander for example...the open up .002 makes the INSIDES all the same size.

The .008 those good quality 22-250 dies had built in as a size down dia was needed to ensure that any brass made in the last 50 years would be sufficiently sized down....if we alter that dia to suit our brass in hand the die works a lot better, and the brass does not get as overworked.

In a perfect world I think we would have a dia that just barely reduced the WHOLE case so it freely fit the chamber, not a sloppy loose fit, but one that allows the gun to breech up without loading the locking lugs excessively (like we get when the shoulder needs bumped) and we would bump the shoulder each time .001-.002. BUT that would require a custom die in many cases...or more easily a custom chamber made to fit an oem die (no extra charge really if you are building a rifle from scratch). Keeping pressures low and just neck sizing, then now and then if need be bumping shoulders with a body die works pretty nicely however.

An easy way to get an idea of your neck tension is to measure a case neck, then seat a J word bullet, and measure the neck again(with the bullet in there), the amount it grows is your neck tension...and pulling the bullet and measuring the neck a final times gives your actual final neck tension(the bullet will size the neck if there is "extra" tension).

And if the J word bullet was say .308 and your cast bullet was .310...if the cast bullet was hard enough your final actual neck tension would be about the same...but the inside neck dia needed to get that tension would be .002 bigger. Generally if you use .0016 as a spring back figure it works out very close....if your neck is .305 inside, and you push a .308 bullet into it, then remove it, you will quite often end up with a .3064 inside neck dia. Somebody (maybe varmint Al ?) quoted that number a long time ago and I have found it to be darn close. So factory dies often have a .308 expander (for 30 caliber stuff) giving us .0016 neck tension.

Bill

[Willbird]

Also something to be aware of on brass from factory ammo, is a so called "factory crimp". I have seen this in a number of brands, It is a reduction in neck dia at the case mouth, not sure if it is a taper or a step...but it survives at least one firing, and gets ironed out as you reload the case several times. On a once fired 22-250 case that has this a .224 bullet(or a .224 gage pin) might be a snug fit at the case mouth...so you really cannot properly measure inside neck dia while this is going on unless you force something (like seating a bullet) into the case mouth, or keep working bigger gage pins (what I use) in til you find the one is actually a snug fit on the whole case neck.

Bill

[HangFireW8]

Also something to be aware of on brass from factory ammo, is a so called "factory crimp".

Bill,

Yes, that's right, the remains of the factory crimp can mess up the whole neck tension equation. The wrinkle (as I call it) can be taken out with a tiny hammer and anvil arrangement, and then running through a conventional full length sizer and expander ball. That, and another shooting (perhaps with a j-word) and then the case can be moved into managed neck tension use.


one thing you cannot keep the exact tention useing the neck as sole unit. The crimp is what is going to make the difference. New brass, once fired , fired 10 times. different brands

I agree. Remains of a crimp, or using a crimp for revolver loads, is going to make a difference.


There is no way to get same neck tention by one die.

I sort of agree. One die, with a bushing sizer and a carefully selected expander, will get most of a good batch into conformity. After that, for the stragglers you may have to swap out the sizer bushing, re-expand, etc. Or, as I do, simply separate them from the batch, and use them as die setup dummies, or FL size them with a conventional die and try again next firing.


You have to use the crimp to control it

I disagree. I produce batches of accurate rifle ammo with zero crimp and consistent bullet pull, and have for years, with both j-words and cast. You just have to be prepared to sort and cull.

The same is true of eccentricity. You'll always get a few in each reloading batch that come out crooked, that doesn't mean you have to shoot them for group with the rest of the batch.

-HF