Seating depth and neck tension

[Bradley Walker]

By ACCIDENT I got a real schooling in neck tension and how it affects seating depth. I shot all 300 rounds of my Lapua brass. I took them out of the box, ran them through an expander, and shot them. After running them through the expander they measured .2665". The outside dimension of the loaded round is .2685". Bullet seating pressure was pretty mild and seating depth was holding .001".

I shot all of these once.

Then I did two things simulataniously. I started to size all my once fired brass with my new Redding bushing die (.266" bushing") and I bought a US cleaner to clean the brass after sizing.

Now bullets would not seat at all... I mean I destroyed some bullets. I use a Wilson seating die, and the bullet was obviously being bulged at the pressure ring at the tip of the Wilson seater.

So, I assumed it was the US cleaner "too clean" and I started in on trying inside neck lubes.... I've tried several... Results were not really very good. Seating depths were all over the place.

Well... I was cruising along measuring stuff and I found out all my sized brass was .264"!!! WTF??? I measured my Redding bushing... guess what it was??? That's right .264"!!! No wonder!!! I believe it is obviously mismarked.

So I ran some brass through the expander again and seated some bullets... back to normal (at least my normal).

Lost stroy short the best groups I get are from properly seated bullets. I think that going from 70-80 bullets to 107s REALLY makes it more important to have that tension right. There is so much bearing surface on the long bullets, they require even less tension.

I am even going to go out on a limb and say the reason light tension seats more consistent is because the seater is micro deforming the nose of the bullet.

 

[ThunderDownUnder]

Bradley, I agree with your observation about long bullets with a lot of their bearing surface in the neck requiring less tension. I have always favoured seating the bullets with as much bearing surface in the neck as possible and have my reamers made to give me chambers that allow this to happen.

I have never considered your other observation about tight necks that require more force to seat the bullets, micro-deforming the ogive. Its worth running a few micro-deformed bullets thru a comparator and checking to see if there is a measurable difference. Could be hard to measure as the best digital calipers only have a resolution of 0.0005" with a tolerance of plus or minus the least significant digit.

It seems Redding must have some sort of QA issue with the marking of their neck bushings because there are a few people I know who have reported incorrectly marked bushings that have caused them some reloading problems. Its not just an isolated incident and Redding should fix the process that allows this to happen.

Ian

 

[BoydAllen]

One thing that is missing from almost all discussions that get into neck tension, as described by the difference in diameters of sized and loaded necks, is neck wall thickness, and how hard the metal is. I do most of my shooting with a .262 neck 6PPC. The necks are never annealed. I have tried brass thickness from .0086 to .0079. With thee powder that I use, 133, more neck tension works better, with the thickest necks I use a .257 bushing. and with the thinnest, a .256. With the thicker necks I have loaded round diameters (over pressure rings) that run around .2605. With the thinner necks the loaded rounds are about .2592. If we were having a discussion of unturned, or slightly turned necks, the bullet seating forces that resulted from these same differences in loaded, and sized diameters would be very different. When I read of shooters deforming bullets with seating stems, my first thought is to wonder why they are using so much neck tension, and whether they have tried using a lot less. Instead, they are usually trying to figure out what is wrong with their seater dies.

 

[Bradley Walker]

I would think you need almost no tension with the long bullets. Geez!!! They have like 1/2" of bearing surface!!!

I would think for my rounds which are not turned or annealed .0005" would be enough expansion. So from .268 od unseated to .2685 seated. Especially after the cases are cleaned with and ultrasonic cleaner.

Btw... All those case lubes did almost nothing to improve the situation for clean cases. I think the solution is use very very little interference fit. The longer the bullet the less you need.

 

[Bradley Walker]

Bradley, I agree with your observation about long bullets with a lot of their bearing surface in the neck requiring less tension. I have always favoured seating the bullets with as much bearing surface in the neck as possible and have my reamers made to give me chambers that allow this to happen.

I have never considered your other observation about tight necks that require more force to seat the bullets, micro-deforming the ogive. Its worth running a few micro-deformed bullets thru a comparator and checking to see if there is a measurable difference. Could be hard to measure as the best digital calipers only have a resolution of 0.0005" with a tolerance of plus or minus the least significant digit.

It seems Redding must have some sort of QA issue with the marking of their neck bushings because there are a few people I know who have reported incorrectly marked bushings that have caused them some reloading problems. Its not just an isolated incident and Redding should fix the process that allows this to happen.

Ian

+1 on the Redding Qa.

The way I figure it the bullet nose deforming slightly is the only thing that can explain the ogive measured differences. On the worst case seating attempts I witnessed the bullet was obviously deformed at the little ring formed by the seater stem.

On the low tension seating attempts (that all seem to be precise measured from the ogive) there is hardly a ring at all where the seater stem contacts the bullet. All attempts were going to the hard stop sO what else could it be?

It makes sense to me. The jacket material near the tip has to be pretty darn soft...

It would be nice to have a seater that pushes at the ogive... Not on the nose.... Since that is where the measurement is taken.

 

[BoydAllen]

Bradley.
Not to be too picky, but the ogive is the entire curve that starts from where the sides of the bullet are parallel, up to the very tip of the bullet. There is some confusion that may come with the use of the term ogive lengh. It does not mean the length of the ogive, or that the ogive is a sepcific place near the bottom of the "nose" of the bullet, but is refers to the length of a loaded round measured from the case head, to somewhere on the ogive, usually near where the rifling will first contact the bullet, although this is not a requirement for the measurement to be accurate and useful, as long as the same tool is used for the same caliber each time.

I think that your idea about the source of irregularities in seating depth definitely bears further investigation, but there are other causes that may combine with the one you mentioned, variations in press linkage stretch or spring being one that comes to mind.
Boyd

 

[lloydx2]

Most factory seating stems are pretty aggressive. They have gotten a lot better in the last 15 years. It was not uncommon to lap the stem with bullet of choice. If done carefully run out can be improved in some instances. Preferably done in a drill press or lathe. You must be carefull not to thin down the walls of the stem to much or it will weaken it. I still do this on some of the newer dies. It works quite well.

 

[Bradley Walker]

Bradley.
Not to be too picky, but the ogive is the entire curve that starts from where the sides of the bullet are parallel, up to the very tip of the bullet. There is some confusion that may come with the use of the term ogive lengh. It does not mean the length of the ogive, or that the ogive is a sepcific place near the bottom of the "nose" of the bullet, but is refers to the length of a loaded round measured from the case head, to somewhere on the ogive, usually near where the rifling will first contact the bullet, although this is not a requirement for the measurement to be accurate and useful, as long as the same tool is used for the same caliber each time.

I think that your idea about the source of irregularities in seating depth definitely bears further investigation, but there are other causes that may combine with the one you mentioned, variations in press linkage stretch or spring being one that comes to mind.
Boyd

In a Wilson die, once the seater hits the stop, there are no other factors except bullet length.

 

[BoydAllen]

When bullets are pointed, the jackets may not take the exact image of the point die, and the shape of the point will vary slightly according to variations in the jackets' hardness. Bob Green makes a gauge that is designed to measure these differences, and with some time and trouble, it may be done with caliper attachment inserts that measure off of the ogive at different points, one where the seater stem would make contact, the other where the rifling first marks the bullet when seated into the rifling. Because of these variations in the distance between these two points of contact, that can occur even within the same box of custom bullets, loaded rounds seating depths, relative to the rifling, can vary to a degree that can be significant to tune, in a high quality benchrest rifle. This variation, and its source are not at all widely known about, or discussed in print, on paper or the internet. I have not spent much time testing whether seating depth variations from this source, and of this magnitude show up on the target, but some have, and they believe that they can be significant to accuracy. Most of us have larger issues to deal with. I certainly do.

 

[Bradley Walker]

Here is an update on the Redding neck bushing that was mismarked.

The .266" Redding bushing measure .264". I re-sized the brass and it came out (you guessed it) .264".

I called Redding and they said that I was measuring it wrong and I could send it to them so they could measure it. He also said my brass is too big and I should size down in two steps.

Um... No.

I bought a WILSON bushing. A .267. I measured it. It measured .2665". I sized a case with it (my brass goes to .271" after firing, my neck is a .272") and the brass came out (you guessed it) .267".

Redding just lost me.

 

[ThunderDownUnder]

Here is an update on the Redding neck bushing that was mismarked.

The .266" Redding bushing measure .264". I re-sized the brass and it came out (you guessed it) .264".

I called Redding and they said that I was measuring it wrong and I could send it to them so they could measure it. He also said my brass is too big and I should size down in two steps.

Um... No.

I bought a WILSON bushing. A .267. I measured it. It measured .2665". I sized a case with it (my brass goes to .271" after firing, my neck is a .272") and the brass came out (you guessed it) .267".

Redding just lost me.

I have always bought Redding TiN bushes and never considered Wilson bushes even though I use their dies along with Redding. I think its time I got some Wilson bushes and put them to good use. Thanks for the info!

Ian

 

[Bradley Walker]

Update:

I used my new Wilson .267 bushing to size half of the neck of my brass that is .271 after it is shot. Resulting in a OD of 268 at the case mouth, and .270 at the base of the neck.

BTW, my loaded round is .2685".

.0005 tension appears to be about perfect for the long 107s and 105s. Now I can seat bullets and the seating stem end doesn't leave a mark at all in the moly on the nose on the bullet. Seating tension is extemely consistent. Keep in mind I don't turn necks so I figure the thicker the neck the less intereference is necessary. I am using out of the box Lapua brass.

Now seating depth is running within .0005" measured with the comparator.

I will continue to use the .267 for 80 and 70 gr bullets but I think the 107 and 105 bullets would be better with the .268"... but we will see.

Once I receive my .268 bushing I plan to size the entore neck on all rounds just change bushings when and if is necessary.

BTW, inside neck lube is not necessary at all once the neck tension is right even after Ultrasonic cleaning. At least that is what I am seeing.