Neck tension - K&M Force Pack

[CacheCropp]

Loaded some rounds on my K&M Arbor with STD Force pack. It was new 223 brass that I FL sized with a neck bushing. I aimed for .003-.004 tension because it’s to be shot out of an AR and I’ve also heard that 223 often shoots better with more tension. They actually came out to be .0045-.005 tension. I was curious to see how much PSI the Arbor Press would register on new brass with more neck tension. Some Of the rounds I seated with no neck lube at all. They showed 70-100 PSI. Then I used Dry lube of the others. They registered a very consistent 23-30 PSI for the next 25 rounds.

My question - so which is the bigger factor in these PSI numbers, the neck tension or the lube and how you apply it?

 

[LRPV]

Long answer short, consistency in seating force and seating depth.

 

[One Eye Pete]

Only my own observation, but neck "friction" from unlubed necks can add more to seating force than neck tension from a tighter bushing using lubed necks. I use a K&M with the standard force pack. Normally I lube the inside of the necks with a moly/alcohol mixture. Anywhere between .002 to .005 neck tension I normally get somewhere between 20 to 40 psi of seating force with fairly good consistency. Very clean unlubed necks will yield much higher numbers with much poorer consistency. My experience seems to agree with your findings.
This all assumes that the necks have a proper chamfer.

 

[CacheCropp]

Ok, but what are we actually measuring with the force pack? If I can line the necks and get consistent 30 PSI with .004-.005 neck tension, I don’t think it’s really telling me much about the neck tension. It tells me how consistent my bullet seating is. Maybe that’s the main point? Not sure.

I will load some at .002 neck tension the same way and see if the 30 PSI drops significantly.

Maybe a better question is - How do you use and see benefits from your Force Pack or similar bullet seating force measurements?

 

[One Eye Pete]

The way I look at it lubricating the necks tends to take away most of the friction encountered when inserting the bullet. This helps the indicator show a truer representation of the force required to expand the brass in the neck as the bullet enters. Theoretically if you sort by seating force you should get better results.
To me the real benefit to the force indicator is it helps me to identitfy rounds with problems, like a bad neck chamfer so that I can put them on the side and use them for warming up the barrel or sighters.
How much all this translates onto the target I'm not totally sure but if I can cull out the rounds that seat with a very noticeable difference in force I feel like I have gained something.
With lubed necks you should see a reduced seating force when you go from .004 to .002 neck tension. (If I were to venture a guess it may drop to 20-25 psi) The other factor I have seen make some difference is if some cases are annealed more than others to the point where the brass is significantly softer.
I guess to sum it up I let the target tell me what neck tension the gun likes and then I use the force gauge to try and tell me that I am getting that same neck tension repeatedly.

 

[mikecr]

As you're observing, seating force does not directly correlate with neck tension.
That's because seating force is so greatly tied to friction, which is independent of tension.
The reality is that we currently hold no means to measure neck tension.

I've been messing with this likely for as long as K&M, and I've somewhat evolved to a different approach.
Instead of measuring seating force with bullets, I measure pre-seating force with an instrumented mandrel.
My necks are friction normalized in that I leave a lightly brushed carbon layer in place. No lubes otherwise.
With this I can see, before bullet seating, comparative tension differences, and then I can adjust each neck to match the rest. When they all match, then I seat bullets.

My adjustment, to get all necks matching, is neck sizing LENGTH.
So if I'm indicating ~5lbs less on a neck, I'll swing over to my Wilson neck sizer and add maybe ~10thou of sizing length, and measure pre-seating force again. It's trial & error until I get a match.
With ~5lbs too much, I'll run the neck through a larger expander mandrel, and resize the neck again and measure again, etc. If this sounds like a pain,, it can be. When it does get to be a pain, I dip anneal necks and start over with the batch.

This works for me because I stay close to brass elasticity. I don't over work it.
Neck tension is spring back force applied to an area (PSI). Necks only spring back 1/2-1thou, depending on cal & thickness. So there is no more force applied after that. It's just sizing (yielding) beyond.
Given this, I don't size necks to 3 or 4thou interference to get more tension.
A normal hardness neck sized down to 1thou interference is plenty, and I can adjust the gripping area of force provided, through sizing length, against seated bullet bearing.

Anyway, don't get caught up into converting tension (gripping force) from seating friction.
There is just no way to do that.
And understand that bullets are not pushed out of necks with firing pressure. Instead, bullets are released from even the tiniest of neck expansion, which occurs with way way less pressure.
It depends on case area, but I wouldn't be surprised if bullets are neck released within 10psi, as with less than a millionth of expansion, a bullet is swinging in the wind.

 

[Fuj]

Too much pressure to seat, may deform the bullet jacket enough
to throw some flyer's, and especially thin skinned hunting bullets.

 

[Scott-ak]

As you're observing, seating force does not directly correlate with neck tension.
That's because seating force is so greatly tied to friction, which is independent of tension.
The reality is that we currently hold no means to measure neck tension.

I've been messing with this likely for as long as K&M, and I've somewhat evolved to a different approach.
Instead of measuring seating force with bullets, I measure pre-seating force with an instrumented mandrel.
My necks are friction normalized in that I leave a lightly brushed carbon layer in place. No lubes otherwise.
With this I can see, before bullet seating, comparative tension differences, and then I can adjust each neck to match the rest. When they all match, then I seat bullets.

My adjustment, to get all necks matching, is neck sizing LENGTH.
So if I'm indicating ~5lbs less on a neck, I'll swing over to my Wilson neck sizer and add maybe ~10thou of sizing length, and measure pre-seating force again. It's trial & error until I get a match.
With ~5lbs too much, I'll run the neck through a larger expander mandrel, and resize the neck again and measure again, etc. If this sounds like a pain,, it can be. When it does get to be a pain, I dip anneal necks and start over with the batch.

This works for me because I stay close to brass elasticity. I don't over work it.
Neck tension is spring back force applied to an area (PSI). Necks only spring back 1/2-1thou, depending on cal & thickness. So there is no more force applied after that. It's just sizing (yielding) beyond.
Given this, I don't size necks to 3 or 4thou interference to get more tension.
A normal hardness neck sized down to 1thou interference is plenty, and I can adjust the gripping area of force provided, through sizing length, against seated bullet bearing.

Anyway, don't get caught up into converting tension (gripping force) from seating friction.
There is just no way to do that.
And understand that bullets are not pushed out of necks with firing pressure. Instead, bullets are released from even the tiniest of neck expansion, which occurs with way way less pressure.
It depends on case area, but I wouldn't be surprised if bullets are neck released within 10psi, as with less than a millionth of expansion, a bullet is swinging in the wind.

That is an intense process and I'll say far beyond anything I will ever strive to achieve.

I write because of the last paragraph, it is interesting. There is a study, I think it was linked on this site, that measured bullet movement during the firing process. Maybe it was acceleration, I don't recall exactly. What was intriguing is that the bullet starts moving at primer ignition, slows, and then speeds up again as the powder starts to burn. Confirming your thoughts.
If that detail was measurable by the average hand loader it seems like we would strive to develop a load where the bullet accelerated without any pauses...

 

[JFrank]

Original question - so which is the bigger factor in these PSI numbers, the neck tension or the lube and how you apply it?

A- the lube was the biggest factor, I leave the carbon in the necks lightly brushed as lube for seating bullets with plenty of bullet hold.

 

[David Christian]

I would argue that the only seating force that matters is a consistent one. Whether they read 10 or 100 psi on your gauge, and whether that was created by lube, the state of the brass, how much carbon you left in the case, to how well you consistently resize, making sure everything is the same case to case is the key. All of the above end up showing at the end when using a seating force gauge.

When I see different numbers when seating, it just means something up the chain is off and not producing consistent results. I then refocus on the steps.

Related to the OP, virgin brass often shows higher seating force numbers. No residual carbon? No chamfer? No mandrel before seating? Various reasons could apply.

 

[BoydAllen]

In the past we have used the term neck tension to refer to the difference in the diameter of a sized case neck before and after a bullet is seated. The assumption was that the force required to move the bullet in the neck during firing would vary with that difference, and, all things being equal it does, for a given neck ID condition, brass hardness, and thickness. Now we have new tools to actually put units on seating force, and again we assume that the force it takes to seat the bullet is similar to the force required to move it during firing. This is further complicated by the use of various lubricants. The only way that I can see to logically deal with all of this is to do tests, and since most of us lack the equipment to measure pressures, do the next best thing and measure velocities. The down side is that testing is expensive and time consuming....but I think that it is probably the only way to proceed.

 

[Lucky6547]

My experience was interesting:
I set up a whidden arbor die such that I thought I would be in the ballpark. I had the standard force pack. I would see the bullet move very consistently at around 45-47lbs, then I would stop when I got to 150lbs because that’s what it was rated for. I was getting a seated depth of about 0.040” longer than I wanted. So I set the die for deeper seating. No change. Setting it deeper and deeper until I thought there was no way I could be that much deeper without it showing a change. I was aiming for around 3.023” but I was always getting around 3.060” +/-0.005”. I had a normal threaded whidden seater die that was already set up for the correct depth that I would compare the arbor die to. Eventually I got frustrated and picked up the die and looked at the gap between the die and the base plate. It was at least 1/8th of an inch!
I had to take out the force pack and readjust the die so that I could apply more pressure than the force pack allowed to get full seating depth with the whidden die. It was quite amazing that if I always stopped at 150lbs, the depth was very consistent.
So do be careful not to assume that if you reach 150lbs that you are going to fully seat your bullet. Perhaps I will need a second arbor press without the force pack to finish seating after observing the initial forces if I want to continue to use the force pack.

 

[JEFFPPC]

I shoot turned necks in both my bench and varmint rifles. I depend on the brushed carbon to be my lube. I have tried lubing and found no benefit. The biggest factor I have found is consistent neck thickness. Brass flows forward, necks get longer, and yes they get thicker. When 45 out of 50 cases are not within 3 or 4 numbers of seating force I run the necks thru the turner. Results are interesting. On some you will think, where did this all come from? From some you will get dust or nothing. The neck thickness does change with every firing. I have found this to make definite difference on paper.

 

[Straightshooter1]

The neck thickness does change with every firing. I have found this to make definite difference on paper.

Hmmm??? When I hear this kind of thing it really peaks my curiosity. Quite some time ago I looked at this and though I remembered I didn't see any such changes. So, I just now grabbed my brass that I've turned and checked to see what difference there might be from when I did that. The Federal .308 brass of mine that has 10 firings on them showed the same neck thickness as when they came off the neck turning tool after the first firing. Likewise, my 6.5 PRC Lapua brass with 6 firings has also not changed in thickness since they were turned.

Now I'm wondering why our two experiences are so different. Could it be due to a difference in how we process our brass? If one is using an expander button in their sizing die, I can see how it's very possible for the thickness to grow as the button pulls material upward through the neck. Where if, like I do, the brass is sized without any expander button and later expanded with a mandrel, then no material is being drawn up; though the sizing process does make the case length slightly longer.

In any case (pun not intended), it's something to keep an eye on. ¯\_(ツ)_/¯

 

[JEFFPPC]

I would guess the fact I am shooting various small 6mm cases with. 262 necks leaving .083 neck wall it shows up. Several folks I have shaerd this with upon checking their necks all reported seeing what I am seeing. Another fact could be loading above 60,000 lb. I use no expander buttons. Only time my cases see a mandrel is when sizing them to cut the necks or expading to .30 for 30 br cases. I figured this out when after I started using a force gauge that as firings increased the seating force increase and became less consistent.

 

[Ranger188]

I shoot turned necks in both my bench and varmint rifles. I depend on the brushed carbon to be my lube. I have tried lubing and found no benefit. The biggest factor I have found is consistent neck thickness. Brass flows forward, necks get longer, and yes they get thicker. When 45 out of 50 cases are not within 3 or 4 numbers of seating force I run the necks thru the turner. Results are interesting. On some you will think, where did this all come from? From some you will get dust or nothing. The neck thickness does change with every firing. I have found this to make definite difference on paper.

Did you find this after 3-4 firings or 5-10?

 

[JEFFPPC]

In as little as 4 or 5 firings including the fire forming. I now go by when the seating force starts to move up. It grows with every firing in my opinion and from what I see.

 

[dgeesaman]

Your last question holds to the classic technical problem that we can only measure seating force (friction and neck tension combined) when we really believe it’s neck tension alone that is more critical.

Many shooters are successful at achieving very consistent seating force, and the dimensional properties of the necks are tightly controlled in other ways. This presumably means neck tension is well controlled. The K&M measures your seating force. Having extremely consistent seating force is a very very good indication that these things are well controlled. Yes, this might set the bar higher than necessary for a very accurate load but it’s this bar or no bar at all.

This is exactly analogous to using bolt/screw torque to control bolt tensile preload. Tensile preload is the critical quantity that makes a bolt work. Unfortunately nobody has invented a way to directly apply neck tension similar to a hydraulic tensioner does for a bolt preload. But excellent dimensional control of the necks, bullets, frictional surfaces, and material hardness (annealing) will allow seating force to get the job done.

Your test shows is also like using a lubricated vs dry bolt torque. Dry has more friction and requires more torque to get the same preload. It is perfectly normal and expected that a lubed neck will seat with less overall force than dry/clean. And whichever gives the most consistent seating force is my preference for building a tune.** If you make this change after the fact you might need to alter your tune.

** for tunes that involve hard jam and/or high neck tension, too much lubrication may prevent from reaching the same tune. A neck can only stretch so far before it deforms and a bullet can only jam so deep before it pushes the bullet in further.

David

 

[mikecr]

The neck thickness does change with every firing.

It doesn't change from firing. It changes with enough FL sizing to roll brass up into necks.
This, accompanied with changes in trim length.
For those of us who minimally size, our necks do not change in thickness once fully fire formed.

 

[JEFFPPC]

I do full length size and I do agree full length sizing contributes. You have a valid point. I am going to shoot up some old rounds in the ppc tomorrow. I will measure before and after when I get to sizing them but that will not be until after I anneal. I don't shoot with anyone who only neck sizes. I did that 60 years ago as a teen. If you read all my posts on this the thickness does not form at a uniform rate. I will ask, are you shooting turned tight neck rounds. If you are and your turner is still set to the final turn, run it down a half dozen and see if you get anything. Read my post number 13 Mike.I actually never measure the thickness, I just run them in the neck turner.

It doesn't change from firing. It changes with enough FL sizing to roll brass up into necks.
This, accompanied with changes in trim length.
For those of us who minimally size, our necks do not change in thickness once fully fire formed.