Case Neck Tension

[big rifle man]

Jimbires, what might be happening is a galvanic type action between dissimilar metals. I've seen that occur on other types of metals. I don't know where you store your ammo but if it's near electrical current that might be the issue. I don't know how old the brass is but I've been told by chemical engineers that over a period of time Brass changes its molecular structure which also might be a cause.

 

[jimbires]

Jimbires, what might be happening is a galvanic type action between dissimilar metals. I've seen that occur on other types of metals. I don't know where you store your ammo but if it's near electrical current that might be the issue. I don't know how old the brass is but I've been told by chemical engineers that over a period of time Brass changes its molecular structure which also might be a cause.

thanks for the info . I couldn't believe how bad these were, when I pulled the bullets .

 

[RiverRider]

Gotta wonder if acid from fingerprints got involved there. I know some guys have to wipe all fingerprints off a gun after handing, otherwise corrosion sets in pretty quickly. I suppose that's a body chemistry thing. Fortunately for me it's not an issue but I have a friend who has to be very cautious about it.

 

[kraky1]

I used to blame it on not getting all the RCBS Case Lube perfectly out of the neck. Now I run a wet heavy duty shop cloth over a small nylon bore brush and get it all out as best I can. It seemed to help a lot but I still got a few cases that had a bit of crack when pushing a year or two later with the seater die. Now I'm starting to wonder if maybe there isn't a little residue from the cleaner additive in my Tumbler that coats into the case neck.... and causes the problem. So now I added a tapered bronze bore brush to the fifth station on my RCBS Case-Mate and I'm scrubbing inside the neck every time I clean primer pockets.
I had a "scratch my head" event a few years ago.... somebody gave me some 25 to 30 year old Federal 270 Factory ammo. The bullets look pretty green and I decided just for fun to pull them and see what the powder looked like. On only about one bullet had the corrosion made it a little below the neckline. ...... and all bullets moved easily with no stickiness after all that time!

 

[truck driver]

I use a Hoppe's stainless Tornado brush to clean the inside of my case necks before dusting with dry moly to ease the expander ball friction when resizing my cases and haven't seen problems with corrosion. Before using the dry moly I would experience case neck stretch during resizing.

 

[greenheadcaller]

Back to the Neck Tension question.

People seem to measure it in various ways and understand it in various ways it seems. No right or wrong answer.

I will say this though, imo .... Once I find the neck tension that is "best" for a given load (and by best I mean the most accurate during load work up and safe in a given rifle), I become very interested/most interested in being able to REPEAT that neck tension over multiple reloading's........and......I find the best way to repeat a given tension, is to batch brass (treating them all the same for life) and anneal every reload. It is hard (for me anyway) to get consistent and REPEATBLE neck tension if some of the brass been shot 5 times before annealing and other have been shot once before annealing. In my opinion, consistent springiness is just as (and some would say more) important than a consistent physical measurement .... but we don't have to decide, we can accomplish both. So, I work up my loads with freshly annealed brass with consistent neck treatment, and once I find the accuracy node, I stick with it and anneal shot brass every time prior to reloading. This is probably overkill annealing if brass life is the only concern, but not overkill if consistent and repeatable neck tension is the goal. Lastly, in my experience, annealing without tempilaq (instead using visual or other methods) can cause huge variances from one lot of brass to the next .... to the point you are better off not doing it all vs doing a poor job of it. With tempilaq, you can repeat consistent tension.

Off the soap box now, there are tons of opinions on this topic, and while I have mine, it doesn't make it the best ... it's just the best for me lol.

Here is an interesting article about neck tension that I found interesting, maybe you will too. http://www.accurateshooter.com/technica ... hing-size/

 

[kraky1]

Excellent Post and reference. Our local gunsmith builds rifles for National Palma shooters. A year or two back I was in the shop and we were bsing about a number of things .... he gave me a sales pitch on neck tension that pretty much matched what you wrote above!

 

[257 Ackley]

Differing neck tension is one of the main contributors to vertical stringing of groups. I don't pay as close attention to all the details on my hunting brass as I do my competition brass, but the steps listed in the above article are important. I found a combo last week while load testing a new bullet for my 6.5X47 at 1000 yards that gave me a vertical spread under 2". Same night another guy shooting a 7 SAUM with 180 hybrids had a vertical over 9". When I asked him about his seating, he admitted some were harder to seat than others.

I use an arbor press to seat all my competition bullets. There is better "feel" of the seating and Wilson dies support the bullet better than any other die I use. If it is harder or easier to seat than normal, put it in the fouler group.

A friend owns a mold making company and deals with specs to the .0000 for most items. He makes his own bushings for his dies after finding that the ID on most bushings can vary by a couple .000 from what is listed on the bushing. I always test bushings on either side of what my loaded round tells me to use for a .002 neck tension to see if more or less tension makes a difference.

The further down this rabbit hole you go, the worse it gets. :roll:

 

[ElmerThud]

The further down this rabbit hole you go, the worse it gets. :roll:

Ah this is so true!

For hunting purposes though, working with fired & anneald brass is far better than with new. The trouble is the time and components wasted getting to the fire formed brass from new..

If you're fortunate enough to have time and range available close at hand, it's not such a bother.
But, if you're an old fart living miles from the nearest available place of safety to shoot, man it's a bind!

In my experience greenheadcaller is pretty much bang on, though I don't anneal at each reloading.
Quote:
I will say this though, imo .... Once I find the neck tension that is "best" for a given load (and by best I mean the most accurate during load work up and safe in a given rifle), I become very interested/most interested in being able to REPEAT that neck tension over multiple reloading's........and......I find the best way to repeat a given tension, is to batch brass (treating them all the same for life) and anneal every reload. It is hard (for me anyway) to get consistent and REPEATBLE neck tension if some of the brass been shot 5 times before annealing and other have been shot once before annealing. In my opinion, consistent springiness is just as (and some would say more) important than a consistent physical measurement .... but we don't have to decide, we can accomplish both. So, I work up my loads with freshly annealed brass with consistent neck treatment, and once I find the accuracy node, I stick with it and anneal shot brass every time prior to reloading. This is probably overkill annealing if brass life is the only concern, but not overkill if consistent and repeatable neck tension is the goal.