Neck tension in general

[Alex Wheeler]

The thing about pressure pushing vs. the neck expanding is it is being taken here as an absolute one or the other. The question is why it could not be a combination of the two. Certainly it does not take a huge amount of pressure to move a bullet as if that was the case, none of use would ever be able to pull bullets from a loaded round. I would guess that the initial movement is pressure pushing and depending on how fast the bullet move out, pressure could also be involved in neck expanding.

I agree, it is not hard to imagine a simultaneous bullet movement and neck expansion. Certainly pressures high enough to Ka-Boom a receiver if completely contained are strong enough to move a bullet through any amount of neck tension AND expand the neck at some point in the process.

Load some cases with a bullet barely in the neck. The neck wont expand. For the neck to expand the bullet needs to create the pressure for that to happen before it moves.

 

[JohnKielly]

Load some cases with a bullet barely in the neck. The neck wont expand. For the neck to expand the bullet needs to create the pressure for that to happen before it moves.

Yep. I recall occasionally using 200SMKs in a chamber throated for 210 Bergers set way out. The 200s ran on .160" jump with them seated .030" in the neck & sooted right down to the shoulder and then some. I could get away with that because I had a .3085" throat.

 

[jlow]

The thing about pressure pushing vs. the neck expanding is it is being taken here as an absolute one or the other. The question is why it could not be a combination of the two. Certainly it does not take a huge amount of pressure to move a bullet as if that was the case, none of use would ever be able to pull bullets from a loaded round. I would guess that the initial movement is pressure pushing and depending on how fast the bullet move out, pressure could also be involved in neck expanding.

I agree, it is not hard to imagine a simultaneous bullet movement and neck expansion. Certainly pressures high enough to Ka-Boom a receiver if completely contained are strong enough to move a bullet through any amount of neck tension AND expand the neck at some point in the process.

Load some cases with a bullet barely in the neck. The neck wont expand. For the neck to expand the bullet needs to create the pressure for that to happen before it moves.

Exactly!

 

[Alex Wheeler]

The point I was trying to make is the neck does expand before the bullet moves, if not the neck wouldnt expand. Also, testing at 1k has show that seating force does not correlate to accuracy.

 

[JohnKielly]

The point I was trying to make is the neck does expand before the bullet moves, if not the neck wouldnt expand.

Not sure that I can totally agree with that or at least, that expansion occurs uniformly irrespective of such variables as seating depth, jump and neck clearance to name a few.

The case I mentioned in my previous post suggests that there was not enough expansion (if any) to seal the case neck from gas passing between it and the chamber wall while the loads that the chamber was crafted for had minimal sooting, suggesting a close case neck to chamber wall fit as combustion passed down the barrel in the latter case. This chamber was a standard (not neck turn) .308 W chamber apart from throat length.

I rarely jam rounds for one particular example, but even so when I did, there was little difference between the soot on those necks and those from the same projectile shot with jump.

All this leads me to conclude that it is likely that a particular condition needs to occur before the neck expands to seal the chamber neck due to the pressure level generated prior to the bullet being ejected. If that start pressure is not achieved then there will be a lesser or "incomplete" neck expansion.

Does that sound reasonable?

 

[memilanuk]

Just curious, for you BR guys that run with high neck tension (zfastmalibu, etc.)... what kind of press are you seating your bullets with?

I ask, because in my experience with both an RW Harte and a K&M arbor press... anything over 0.002" neck tension pretty much obliterated any 'feel' and as much as you guys are talking about made it difficult to get a repeatable seating depth. I'm guessing thats not an issue for you, so like I said... I'm curious... how are you doing it?

 

[Joe R]

Daniel.308 said:


Quote from: Joe Salt on Yesterday at 08:44 AM

I'm with Matt and Webster on this, At 1000 yards you can see a difference between a tight neck and a loose one! So that tells me you have more pressure because the neck has a tighter grip on the bullet and therefore it holds the bullet in place longer while building pressure. So I belive this is a factual answer!

Joe Salt


I agree with that because I've seen it myself.

Count me in on this. I know this is a fact.

I use mandrels to expand my 308 necks. I polish them down to .0001 precision because that's what it takes to get the neck tension that I want. I use a hydra press to measure seating force, so I know from first hand experience that .0001 difference in mandrel size makes a difference in seating force, velocity and on the target.

The bushing sizes of .001 are way too gross to get the accuracy, low SDs and ESs for 1K yards. I've always turned the necks to .014 and I thought I was doing well, but after taking Ben Steinsholt advice and go down to .012, I've seen improvements and I'm a believer now that I've seen it.

Mike,
just because you can't measure something directly doesn't mean that you can't measure it at all. That's what the hydra press does indirectly. And talk to any astro physicist (my wife's cousin is one) that's the only way they find new stars these days. They measure indirect influences on their point of observation. Physicians do the same thing all the time with an EKG. They measure blood pressure and heart rate to determine if there is blockage and how much. If there is then they pump die in to find where the blockage is, etc...

Kindest regards,

Joe

 

[DanSavage]

Thanks for sharing Joe,, This is science class!lol

 

[TC260]

I agree, it is not hard to imagine a simultaneous bullet movement and neck expansion. Certainly pressures high enough to Ka-Boom a receiver if completely contained are strong enough to move a bullet through any amount of neck tension AND expand the neck at some point in the process.

That's what I would guess too. Everything about the process is non-linear so that doesn't generally lend itself to a nice clean clear-cut sequence of events.

 

[savagedasher]

Neck tension . Is a term that shooters use. To me it isn't necessary to have if your single feeding a bullet that you are jumping. My bullets I jump .025 and only use half the neck for tension. .063 to .066 bushing has no effect on speed or ES or accuracy. When I shot bullet that was in the lands It was a must.
as far as soot down the neck that is caused by how soft or hard the brass is.
If you are jamming or putting more then one bullet in the gun you must have more neck tension. Larry

 

[DanSavage]

A top shooter I know soft seats his bullets and has great accuracy. This is done by using light neck tension and loading long. When the round is chambered the bullet touches the rifling and the as the bolt is closed the bullet gets pushed back into the case a little bit. He states that it puts the bullet in the same spot every time.

 

[amlevin]

A top shooter I know soft seats his bullets and has great accuracy. This is done by using light neck tension and loading long. When the round is chambered the bullet touches the rifling and the as the bolt is closed the bullet gets pushed back into the case a little bit. He states that it puts the bullet in the same spot every time.

As long as the chamber is just as clean as when he loaded his first round.

 

[dkhunt14]

A top shooter I know soft seats his bullets and has great accuracy. This is done by using light neck tension and loading long. When the round is chambered the bullet touches the rifling and the as the bolt is closed the bullet gets pushed back into the case a little bit. He states that it puts the bullet in the same spot every time.

I have seen guys do well at 1000 yard BR doing this. I have also seen it give big vertical fliers. If you get carbon or dirt in the throat from firing a string the depth changes. Also if it hits the barrel going in the bullet gets pushed deeper. I prefer to have enough tension to hold the bullet from moving. In tests at 1000 most of my guns preferred more tension. Matt

 

[Link]

A top shooter I know soft seats his bullets and has great accuracy. This is done by using light neck tension and loading long. When the round is chambered the bullet touches the rifling and the as the bolt is closed the bullet gets pushed back into the case a little bit. He states that it puts the bullet in the same spot every time.

Wouldn't any little thing that caused inconstant neck tension give different overall lengths ?
Like hardness of neck brass, Carbon in neck, etc.

Link

 

[mikecr]

On grip-vs-pull, my testing shows(me) that bullets are released under pressure and not overcoming friction:
Roughen squeaky clean necks and notice increased seating forces on seating clean bullets.
Lube necks with Tungsten Disulphide(WS2) and notice seating forces of same bullets is reduced.
Fire the groups together over a chrony and notice no difference in MV.
Yet, I can increase MV by increasing actual neck tension, regardless of seating friction(which I can control no matter the tension).
Conclusion; Seating friction/inferred pull, means nothing to bullet release.

On sooting; this is affected by a combination of brass thickness/hardness, neck length, load pressure, load timing, cleanliness and clearances(including end clearance).
It can't easily be isolated and applied to the subject here.

 

[BenPerfected]

Mike,
With all these variables, how can I measure which ones are really important?
Ben

 

[DanSavage]

I've been doing well running a nylon brush in and out of the neck on a fired case and running .001 neck tension. This method seems to be very consistent with giving a smooth seating force and uniform seating depth. I single feed only though.

 

[Alex Wheeler]

Mike,
With all these variables, how can I measure which ones are really important?
Ben

You test. You will never be a top shooter if you dont do the work for yourself. Dont take anything that any of us say as gospel, do you own testing and you'll learn even more than anyone can tell you. The best shooters a know test 10 times more than the average shooter. It has nothing to do with a lucky barrel, bullets, range, or money. Its all about who puts in the work.

 

[BoydAllen]

There is only one test that matters, the target. Although I am not at all against theoretical discussions, they have their limits when it comes to predicting results. IMO testing is always the best approach...because it solves the issue of incorrect imagination of what is taking place. The target, and chronograph will generally tell you the truth, and if that does not jive with your theories, change the theory.

Recently I have been working with a fellow who is making a good start with his first accurate rifle. The one thing that I am working to break him of is eliminating possible solutions by reasoning alone. I think that this is all to common, and would readily admit to doing it myself.

The most recent example of this is what I have learned about finding the best seating depth when jumping bullets from a section in the Berger manual, around page 202. It is completely different than the assumptions that I previously operated under. Don't assume...test, then you wil really know.

In the short range game, bushing selection can effect tune, more or less depending on the powder being used.

 

[mikecr]

Mike, With all these variables, how can I measure which ones are really important?

What variables, and what is important to you?

What's important to me is understanding.