Neck tension.

B

BJS6

Guest
A lot is said at times about neck tension. The actual amount, the consistency and annealing the cases. Sounds like it is a big deal.

I have tried different bushes within the range of sensible sizing to create different neck tensions of between 1 and 3 thou. I have never really noticed any real difference in accuracy as a result of the varying neck tension. That said I am using a decent jam and not a light jam or maybe even a jump. Does that have a bearing on the matter ?

What I have noticed is that the lighter neck tension results in less loaded bullet run out and if there is any accuracy change at all it favours the lighter tension that results in less run out. Is it the lighter tension of the lower runout that helps ??

Even when using a good deep jam with ultra's a 1 - 1.5 thou tension seems to be enough to shove the bullet in without them sliding back in the case. I am using a 0.2682 loaded diameter at the pressure ring in a 269 chamber so the case neck walls are in the order of 12.5 thou thick.

One other comment/question. The tension is usually talked about in terms of bullet seating force but called "neck tension". The tension that really matters is the force needed to pull the bullet out of the neck not that needed to push it in. Has anybody looked at the correlation between the force to push the bullet in the case neck and that needed to pull the bullet out ?

Thoughts/commenst ??

Bryce
 
Mmm...

Bryce,
I think Jackie uses a 265 bushing with his 269 neck, lots of 133 and Ultras. It works for him....
If you don't think it makes a difference, then pick an arbitrary tension and then shoot it.
Many people spend far too much time thinking about stuff which is not really important. Find something that works and leave it alone.

As I told you, I found a load that worked some time ago and have not changed a thing since. Same seating depth, load, bullet, tension etc. Heck, I even threatened to weld my Harrells up..... we should worry more about how the hell we shoot the wind on that Nelson range!!! When we can figure that out, we will have it made and Ian Owen will have to watch out..... :)))

Have a good one.
Peter
 
It takes more pressure to start the bullet into the rifling lands than it does to expand even a thick neck.......necks are DESIGNED to seal (open up and slap against the chamber walls, completely releasing the bullet) before the bullet gets out of the neck.


think about it ;)


al
 
al,

I can't argue with you in regard to BR applications, but when I'm loading 200 SMKs .035" into the case neck with my 1200 yard gun, I'm going to end up with soot on the neck to the shoulder & that's with a neck that's only a thou or two looser than the average BR standard to allow for the risk of crud you might encounter shooting off your belly. That projectile is off & going long before there's significant neck expansion. Admittedly, they're jumping more than a tad because the guns are chambered for the 210s.

John
 
BJS6 said:
One other comment/question. The tension is usually talked about in terms of bullet seating force but called "neck tension". The tension that really matters is the force needed to pull the bullet out of the neck not that needed to push it in. Has anybody looked at the correlation between the force to push the bullet in the case neck and that needed to pull the bullet out ?
Click to expand...
Yes, there was an article in Precision Shooting a while back, but it was by McPherson. Best I remember, bullet pull went up or down with respect to time and moly coating. That is, if it took 50-inch pounds to pull a bullet one hour after it was seated, it might take 70 after 4 hours, 80 after a day, and 100 after a week. Those numbers aren't accurate, just "for instance"

Moly coated bullets had a more even pull over time, and of course, were less for a given neck sizing. McPherson is a moly advocate I believe, & it is just human nature to get better results with what you believe in (why tests are best done "blind"), so take this for what it's worth.

The hardness of the brass will also affect neck tension -- you'll get less or greater tension than with virgin cases, depending on whether you use a bushing or "oversize" & then expand back up (traditional die).

I've never found it all that critical, but then my tests weren't very scientific, either. It does take a fair bit of neck tension to keep the bullet from being pushed back in the case if you are using a significant bullet jam, but once you've got that, I've never found any difference. Your mileage may vary.
 
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Thanks for the comments guys.

I am pretty happy that I have figured out what works for me but wondered if others had comments, especially with respect to the differences in neck tension between thin and thicker necks and work hardened brass. Seems to me that a lot of emphasis is put in pushing the bullet in when in reality that may or may not be an accurate representation of what it takes to pull the bullet out ! Work harened necks certainly seat easier for a given bush but does that equate to a change in the realease tension ??? I dunno, never tested it, they don't seem to shoot any different to fresh brass for me !!

Also seems that there is a more or less direct relationship between the amount of neck sizing and the amount of expansion on seating the bullets and the magnitude of the loaded round runout. Using a lot of tension to achive one purpose will at some point start to impact on runout which obviously will undo some of the good that the greater tension may have done.

Al, I did think about it. Perfectly logical that if you jam hard enough the neck won't matter a damn. However to get that jam you need a certain degree of tension or the bullet will just move instead. At some point in seating depth the neck tension must become the dominant factor or at least a lot more important, like the effect a crimp has in certain loads. SUre the neck seals off before the bullet is fully beyond the throat but that isn't to say that the resistance to the bullet moving, as effected by neck tension, doesn't have some impact on the early pressure build up, again just like a crimp.

Peter, I sure hear you about the wind ! I swear I help upwind into a left to right and had the shot actually go left of the crosshairs, something spooky going on there !!! We'll have to have a get together at Tokoroa maybe and "think tank" about wind reading and how to beat that Owen character, and Kevin, Tony, Graeme ....... !!

I am not getting all concerned about this stuff, my rifle is going good, as much trying to make some talk about something that isn't freakin tuners or these Americans B****!ng at each other because they have been cooped up all winter !! Glad we can shoot all year if we don't mind chancing getting wet !!

Cheers guys

Bryce
 
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Bryce,


We're still a page or two off from each other.......


I'm not talking about "jam", I'm talking about the next step beyond jam.....actual engravement or entry into the lands.


The work has been done, the tests have been run..... It takes MORE PRESSURE than the neck can withstand before the bullet can even START into the actual lands. For many people the primer blast alone seats the bullet deeper than they did! But for anyone A'tall one simple fact remains........the bullet moves forward and STOPS until pressure builds, the neck opens up and seals and THEN the bullet finally gets going again. Even with a running start ("jumping" the bullet) it's hard to keep the bullet going. A long freebore like Weatherby and a tight crimp on the bullet MAY give the bullet enough momentum that it only slows down instead of actually stopping, but for your typical accuracy setup the bullet is setting there at a dead stop, the neck slaps open and the bullet takes off. With slow burning powders the expansion is slow enough that some powder gas leaks around to stain the neck, even clear down to the shoulder before the neck seals.......but the bullet is STILL setting there at this point because it takes 12,000psi to start the bullet into the lands but only 5,000-9,000psi to expand the neck.


Ain't no magick aout it.


((((( Someone please proof my numbers because I'm setting down at the hospital wasting time while my wife is being induced for birth :) They just restarted the Pitocin drip.....I don't have my reference materials close to hand and the nurses are clueless.....))))))



LOL


al
 
Makes perfect sense Al, I knew what you were saying but in typing my response I kinda went off track thinking about another aspect of it. Sorry.

In light of what you are saying about the bullet stopping it is hardly any wonder that my varying the neck tension hasn't achieved a damn thing !!

BUT ...... how is it that seating the bullet to 20 thou over just touching shoots a whole lot better than 10 thou over or 5 thou over ?? Seems that effects the initial pressure build up. Bullet doesn't move as far until the rifling forces it to stop and so the pressure builds a smidge faster ????

I had a 204 Ruger in a Kimber ..... shot best with a 0.060 - 0.100 jump, more bullet movement before the bullet stops slows the initial pressure build up ???
 
Bryce, when you seat a bullet .030 longer (for example) than where the bullets 'just touch' the lands, that doesn't mean that the bullet physically ends up pushed .030 down the bore when the bolt is closed. No amount of neck tension will allow this to happen. When I refer to a bullet being 'jammed' a certain amount, it's relative to the 'just touching' point.

Here's something you might want to do: try to push a jacketed bullet down the bore sometime with a wooden dowel. Then think about the force needed to do this as relates to neck tension.

'Course, this little test also illustrates the difference between rimfires and centerfires. Kinda' makes the whole situation with tun.....ooops!!! :eek: I almost said the 'T' word! ;) :) :D -Al (notin wa)
 
alinwa said:
((((( Someone please proof my numbers because I'm setting down at the hospital wasting time while my wife is being induced for birth :) They just restarted the Pitocin drip.....I don't have my reference materials close to hand and the nurses are clueless.....))))))al
Click to expand...

Al, congrats! Yeah..once the Pitocin starts, you're roundin' 3rd. and headed for home plate. Best wishes to you and your family! :) -Al
 
Al Nyhus,

I sure hear what you are saying.

I use the just touching as a reference point also and establish the seating + or - from there, plus in terms of my BR rifle.

I seat Ultra's at +20 thou, that is where they shoot best for me. Due to the shape of the bullet and how they wedge in even a moderate neck tension of around 1.5 thou will hold the bullet at that length. I can measure a round, chamber it, remove it and remeasure it and the bullet has not been pushed back, of course it has 4 land marks on it that are about twice as long as they are wide.

You'd have seen the same deal with high number ogive 30's I guess ??

Obviously low number ogives will behave differently since they will just bump up and stop a lot sooner.
 
I have done a bit of this

I use the point where the bullet just kisses the lands as my starting point to tune. Often when I begin to find this I will have to back the stem back .015 or so from where I first seated the bullet, with moderate tension, to get back to where the bullet just kiss the lands. I have a 30 BR barrel that is in tune when the bullets are seated .015 into the lands. I use .004 neck tension, pretty much. Soft necked cases will hold the bullets to engrave that much into the lands. I don't know how much more but .015 I am sure of.

When I first started shooting Score BR I bought a used rifle in 30-HC. It is a 30-30 on steroids. I was instructed to "Jam" the bullets HARD and adjust the powder to find my tune. I did that, It worked. I have since gone at it differently, selecting my load from crono results and using seating depth to find my tune. I prefer the latter. I have had success doing it.

A shooting buddy; traveling companion has had great results jumping his bullets. His last barrel liked.009 off. It shot a round hole there. He also found that a .001 variation would throw it out of tune there. He is jumping them in his new barrel now with the same good results. He never has to be concerned about opening his bolt with a loaded round in. ;)
 
Al Nyhus,

Reread very carefully to see that I said REstarted the Pit!!!! :(:(

We're on our second day here, the Pit's on full bore and the contractions just stopped again for the last 15min.........


LOOONGgggggg boring story but suffice it to say that we aren't expecting to round home for a while yet :):)

Thank You for your thoughts.

Al (in) Wa
 
Congratulations in advance Alinwa !!

All the best to you, your wife and the baby, hope it all goes well.
 
Hangin 'bout bored but I am pretty sure you have the easy job !!! :)
 
Bryce

I shoot Ultras and Bruno 00 Boat tails the same way. A .265 die with a .269 neck, seating the bullets out to where the marks appear about twice as long as they are wide on a .237 4-groove Krieger and a big dose of N133.
As you have discovered, the bullet really doesn't get "tight" in the lands, because the double radius design fits a 1.5 lead angle about perfect. This is the way they shoot for me,and justr babout every body that has tried this say that it really wakes that design of bullet up.
This, however, does not seem to work with other powders, such as 322 and 8208. It seems to be a weird quirk of N133 when using this style of bullet.........jackie
 
Take care of them when you get'em home Al !! Get back and hold her hand rather than be chatting here !! :)


Jackie, I kinda started from scratch with load development when I got the rifle but had your posts in the back of my mind re a jam and a big does of N133. I went down the normal path of testing and so on but eventually ended up right where you suggested would shoot. Kreiger 4 groove, good jam, 265 - 266 bush and 30 plus grains N133. I have two new Kreigers and a friend has another and they all respond to Ultra's and N133 exactly the same, actually all seem to like right on 30.1 grains, at least on the days we were testing.

Thanks

Bryce
 
Bryce,

I've got a laptop, the hospital is Wi-Fi'd......I just come back on when the nurses are all huddled 'round like right now :) I'm looking at 2 nurses and a doctor as they haggle over the monitors. I wasn't on at all yesterday.....

Some of these posts have set up on the screen for hours, several I've dropped or rewritten because I've forgotten where they were.

I'm just using this to stay awake, it's going into the second nite now. They say the brain shuts down last, we might find out..... :D


LOL


al
 
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