neck tension

[Larry Ross]

My reloading process is;
tumble to clean, full length resize and deprime, trim to length, with my case prep station, champher inside flash hole, brush primer pocket, brush inside of neck, champher inside and outside of neck. Then I prime, throw powder and seat the bullet.

I have a RCBS competiton resizer and bullet seater. Overall length using the Hornady O.A.L. gage is
3.344. My loads are producing 1" +/- at 300 (not great by some of your standards I know) I am using Rem. brass and primers. I am shooting a Rem. 700 308 in F/TR, 175 SMK

You guys talk about neck tenson, could you tell me more about that, how you do it, how you measure it, etc.

Thanks for any info.

Larry

 

[DennisH]

You will need a FL neck bushing die. This is what I use, some use just a neck die.

After seating a bullet in your case fired from your gun, measure the neck. If it's .285 (just an example), you need a .283 bushing for your die, there fore you will have .002 neck tension. If you want .001 tension, you will need a .284 bushing.

IMO .001 is a little loose and could cause problems.

If you jam your bullets, you may want more neck tension. When chambering the bullet, if the neck is to loose, you probably will push the bullet more into the case. If you have a misfire and need to extract the round, the bullet may stick in the lands. You will have an action full of gun powder and a bullet in the lands.

Some also use an inside neck mandrel first then size.

 

[Larry Ross]

I did not know to mention it, but my gun has a long throat. I am jumping about .038. So right now I don't know what my neck tension is, is that correct?

lr

 

[DennisH]

Larry,

The only way to determine neck tension on your gun is to follow the procedures I listed above.

Good Luck, Dennis

After seating a bullet in your case fired from your gun, measure the neck. If it's .285 (just an example), you need a .283 bushing for your die, there fore you will have .002 neck tension. If you want .001 tension, you will need a .284 bushing.

 

[Larry Ross]

I understad, thanks for you help.

lr

 

[jbpmidas]

To measure your current neck tensio, just measure the outside of the neck before you seat the bullet. Then measure it again after seating. The difference is your current neck tension.

 

[lpreddick]

totally agree with above. i am not a competitive shooter, butt i am an ACCURACY NUT! i read all i can on this site and have learned more here than from all other sources. i suspect that VARIATIONS in neck tension and VARIATIONS in seating depth affect accuracy more than most other variables that we can control. there are several threads here concerning neck tension and dealing with it can be a struggle sometimes, esp when it changes over time after loading...my latest wild hair.

 

[Elkbane]

Larry,
DennisH has provided ONE WAY to control neck tension, but it's not the only way (Dennis, don't take this as a slant to you, your description is accurate).

When using F/L dies, it's instructive to have four measurements: 1)the neck OD of a fired case, 2)the neck OD of a sized case with the decapping stem removed from the die, 3)the neck OD of a sized case after expansion (i.e. decapper/expander installed), and 4) the neck OD of a loaded round. With these measurements, you can determine what type of sizing die will best "fit" your situation. The difference between #4 and #3 is your effective neck tension.

If the difference between the fired case and the sized case is greater than about 5-6 thousands, using bushing dies may produce more runout on the neck than you're willing to accept, or you may have to size down in two stages to keep the necks straight. On some of my factory rifles, I have 10-12 thousands of difference there, so I use non-bushing dies (typically Forster F/L) in those instances.

Knowing the difference between fired case and sized case without expander lets you know how much you are "working" the brass during resizing. You want as little reduction as possible, but enough to provide the neck tension you are looking for. In some cases, where the die is over constricting the neck during sizing, you may need to get the die neck honed out to a larger diameter. Forster offers tis service for a minimal fee - other die manufactures may as well.

If you just need to change (increase) neck tension with the die you currently have, you can chuck the whole decapping stem in a drill motor and turn off a thousand or so by holding the expander ball between your fingers with 320 grit sandpaper. If the expander is cylindrical, keep the sandpaper moving longitudinally while you turn the stem to keep the shape cylindrical. You don't have to turn it very long to take a thousandth off the diameter- check you work frequently until you get the measurement you want.

WHatever you do, I'd settle on a brand of brass first before I did much die modification as the neck wall thickness will come into play, especially before having a die neck honed out. If you are considering changing to diferent brass, I'd do that first
Elkbane

 

[Larry Ross]

Thanks to all of you that got back to me on this. Some of it is a little over my head right now, so I'm going to print these comments so I can study and digest them.

Thanks again

Larry

 

[XTR]

There are a lot of ways to get there, I take the easy way and use a Lee collet sizer for my 308 loads. My F-TR rifle holds .25MOA vertical at 200 yards that way.

Maybe you can get better doing all the other work, but I have other things to do and the dies are only $28.

You may not be able to read it in the pic, that group is .710 inches max, .638 wide and .312 tall. That's not a rare group. I don't do short range shooting with that rifle often.

 

[BoydAllen]

Getting back to the original question, the common definition of neck tension is the difference in sized and loaded neck diameters, measured over the bullet, BUT the real source of ballistic uniformity that stems from this area is uniformity of the force that it take to move the bullet as it starts forward during firing. This is not so easy to measure. Normally, about as close as we come is to notice how much effort it takes to seat bullets, and how uniform that effort is. This is easier to feel using an arbor press and seating dies that are designed for that type of use. The much greater leverage of regular reloading presses tends to mask these differences.

Before you get too far into fixing your loads, let me say that it seems to me that you are getting excellent accuracy if you are able to achieve an inch at 300 yards. How much of this is vertical? I ask because that is the dimension that would possibly (There are other issues that come into play for the reduction of vertical in groups.) be improved by more uniform bullet pull. Because of .308s recoil in rifles of ordinary weight, and some other factors like chamber design of factory rifles, I would not expect to do much better than you are in any case. I think that most any tactical , highpower competitor, or hunter would be well pleased to have a .308 that performed as yours apparently does. Short and long range benchrest competition do not see many .308s these days, because there are more suitable calibers for those types of competition. I started out reloading with a .308, and learned a lot in the process. Because mine only liked the heavier bullets, I had to learn a level of concentration ( to deal with the recoil in a light rifle) that has come in handy over the years. I hope that you enjoy yours as much as I did mine.

 

[Larry Ross]

XTR;
I have the Lee Delux Die Set in 308. I tried reloading with the collet neck sizer when I first got it but did not like how the results, so I got the RCBS competion dies and that is what I have been using. Are you saying the collet die will accomplish this consistant neck tension issue? The collet die has a decapping pin, so do you use it instead of my full length resizer?
As I remember (year or so ago) I got some buckled shoulders, I just had troube using the collet die.

Larry

 

[Larry Ross]

Boyd;
Thank for your post, it is really nice to hear a plus from someone. I bought my 700 308 in Feb of 2010 and have been messing with it ever since, bullets, powder, seating depth, scope, insert for scope rings, dies and I don't know what else (so what is different from anyone else, right. Another way of putting it "don't feel like the Lone Ranger")

I have just upgrade my scope (yet to be put on) to a Nightforce BR 12 - 42. Main reason for the expenditure was I could not see very well to tell how much to hold over if I got into the 8 or 9 ring from 600 and 1000 (been using a Burrs 6.5 - 20 FF11 Tact, really like the scope but think it is the wrong one for what I want to do)

On the bullet seating, I don't think I can really feel my bullets being seated, I will start paying attention to that and see if I can feel any differences.

On my groups, I just switched from 155 SMK to 175 SMK. My first outing I loaded 6 different loads, 43.8 Varget gave me (at 300) 7/8 vert and 5/8 horiz. I made another trip to the range week later to see if that was a fluke. Two groups, one was1 1/16 horiz and 1 3/8 vert the other was 3/4 horiz and 7/8 vert. So I think I am set for now with every thing I am doing, except maybe for this neck tension thing. After looking into the price of those dies,that is going to have to wait for a while. After all, at some point (and this is a "to each his own thing") this chasing for one hole can get beyond reason. For now with my new scope, I probably need to spend more time improving my ability to shoot better.

Larry

 

[amlevin]

Getting back to the original question, the common definition of neck tension is the difference in sized and loaded neck diameters, measured over the bullet, BUT the real source of ballistic uniformity that stems from this area is uniformity of the force that it take to move the bullet as it starts forward during firing.

This is my understanding as well. I have also read that regardless of the amount of "neck tension" one creates by neck sizing below bullet diameter, the end result is that when you seat the bullet it merely becomes a sizing ball/mandrel (although not as good as the real things) and the "net" tension is considered to be that of .001" to start with.

I've been told numerous times by people that shoot far better than I that it's not the "amount" of neck tension that's important as much as the fact it needs to be uniform.

 

[BoydAllen]

Based on a lot of experience, I would have to disagree with that. While it is true that after a certain point, the bullet acts as an expander, and no further grip is exerted, there is a range where this is not the case. For my .262 neck 6PPCs this range is between .001 and .003. Within this range I can see differences in accuracy, depending on the powder used, and if the bullet pulls were all the same, I do not think that this would be the case. Also there are other issues.

Back in the day, I was loading uncoated bullets for a .220 Swift, sizing cases with a Lee collet die. The neck tension was on the light side, but the bullets were secure, and the accuracy was good. When I tried moly coated bullets, they were not sufficiently secure with the same sizing, so I ordered a new mandrel that measured .001 smaller, and the the problem was solved. Obviously there was a difference in bullet grip. I went through the same thing with sizing bushings for a tight necked .222 when I made the switch to coated bullets. I should add that I gave up the coated bullets, but kept the slightly heavier neck tensions, and the accuracy stayed good.

Every so often, when I try a new powder, I do a neck tension test, starting with just enough to hold bullets, checking for accuracy, to see what the minimum tension is for best accuracy. The reason that I do this is that if I can get away with less sizing, it is easier to assemble straight ammunition, particularly with flat based bullets. Going way back, I can remember a one pound bottle of old 2015 that shot very well with light tension. When I bought an 8# jug of some later production powder, it was not the same, so a friend got a real deal, and his .22-250 really shoots well with what my PPC only found to be mediocre.

Over a decade back, I was using medium tension on my PPC (with 133) ,and a friend (who was a very accomplished shooter and bullet maker) told me that he and his shooting buddy had found that using more neck tension (.003 or a little more) gave better results. I changed bushings, and saw an immediate difference.

Later, I changed to a custom seater, partially because the greater tension needed the tighter fit to seat bullets as straight as I could with less tension with an off the shelf seater. Although I am pretty sure that this change showed up on the targets, it was not nearly as dramatic a difference as one sees with normal tuning.

 

[amlevin]

Based on a lot of experience, I would have to disagree with that.

Can I add you to the long list of people that disagree with Richard Lee? 8)

 

[fguffey]

Larry Ross, You have put them in a bind, there is no such thing as neck tension, there is interference fit, crush fit and the difference between the diameter of the bullet and inside diameter of the case neck.

I can measure bullet hold, bullet hold is measured in pounds, I have been told Aberdeen Md. build a high dollar tester, no matter how expensive the design they did not measure neck tension. They did managed to explain ‘cold welding?’ as a reason for bullets wanting to stay connected to the case when fired. The expensive design was caused by ‘bullet pull’, their desig pulled the bullets out of the case.

I measure bullet hold in pounds, if a reloader/bench rester can not afford a bullet puller that measures in pounds try to build a bullet pusher. I use old parts and pieces that are used for other purposes.

The Aberdeen Proving Grounds in Md. were not reloading and testing, they were testing loaded ammo from storage, it is claimed some of the bullets pulled required 500 pounds to remove, but, there was no problem created with high pressure when the cases were fired. Had they read R. Lee’s book on modern reloading they would have had a hint, there is no such thing as too much crimp, seems ‘time was a factor’ or ‘time is a factor’.

F. Guffey

 

[BoydAllen]

I don't think that the recent discussion has been about whether bullets bonding to necks is going to blow up rifles, but that accuracy would be adversely affected, and what causes bullet pull to dramatically increase (in some cases) over time. Current military ammo may not have it, but I believe that some of the older .30 caliber stuff had the inside of case necks coated some sort of asphalt sealer. I think that among other things this might have prevented the forming of a common layer of oxidation between bullets and case necks. In any case, the differences in tune that I wrote about that are associated with small differences in sized neck diameter, (of cases that have turned necks) might not be noticed by someone loading for a typical hunting or military rifle. The 500 pound bullet pull information was very useful to help dispel the doubt that some have as to whether some sort of bonding does in fact take place. At the end of the day, we are still left with the question of how to avoid the problem. My solution has been to not load very far ahead of my shooting schedule, or if I do, to seat bullets longer than can be chambered without undue force, and then finish seating them before they are to be shot. As always, more information is a good thing.