Neck Tension

[Mulligan]

This is interesting
CW

 

[PracticalTactical]

Thanks for the reply. I do not turn necks but control neck tension similar to what you describe. I would like to know if my efforts have any measurable effect on accuracy. I could do the testing and data analysis if I choose to do that, but it is a lot of effort since it takes a lot of data to define small changes. So, I thought I would see if someone else had done the testing and analysis even if it is on a different cartridge. I prefer data over opinions but sometimes opinions are all we have unless we are willing to do the testing. Thanks again for your reply.

This brings us back to my original point... Neck tension is just one of many other variables.

The effect of neck tension variance however small is obvious at a theoretical level. It is a variable and will have an effect.

In this sense the variance result is not something predictable that can be cast with a broad brush to all who reload. How much neck clearance you have will be a factor, how much freebore diameter clearance you have will be a factor, how much jump you have will be a factor... etc.

Taking this even further, you will need to get into the effect of cold welding. A process of corrosion that occurs between the brass and copper that fuses the two components to each other over a period of time. This is why long range guys seat bullets too long and re-seat the day of the match. This breaks the cold weld.

The real question is whether or not your rifle and hand loading process is good enough for you to detect any of these differences.

I would also suggest that you consider how neck tension variance might affect "accuracy" as framed per your original post. POI accuracy on target? or muzzle velocity variance? I doubt neck tension is going to meaningfully change POI unless that POI variance is the result of muzzle velocity variance. In other words, you will find your answer in the velocity spreads.

 

[CharlieNC]

Looking forward to learning more from this thread. Besides correcting a gross problem with annealing, I've done nothing to evaluate improvements with neck tension.

 

[Petros284]

One factor to consider when testing out various rates of neck tension is the powder you are using. Many have found that with slower burning powders especially those in larger magnum cases etc that more neck tension has proven to perform better than light tension. The theory behind this is that a more complete powder burn occurs because of the extra split second the bullet is held. This can be evidenced by carbon on the necks of the case after shooting them. With more tension, there is less carbon and the numbers on the chronograph and on paper seem to be better. Just an observation.

 

[rwj]

The hard part in coming to a definitive conclusion with regard to any single variable in the reloading process is that we are always testing the sum result of all possible variables.

The biggest mistake we can make is assuming the variable we are thinking about is solely responsible for the results produced.

Variables most certainly interact… it is what led to creating designed experiments (Taguchi) where multiple variables are changed simultaneously to evaluate their relationship. This interaction can be hidden when only changing one variable.

 

[gunsandgunsmithing]

Not taking a side further but this was a good conversation. MKS in this thread is a sharp guy. Haven't spoken to him in a few years now but I believe he was a mechanical engineer but he was/is a professor at the University of Louisville. He may be retired now. He does bring a scientific approach to how he feels neck tension works, fwiw. It's not terribly long. Good read, still different opinions though.

When does the case neck expand? [Archive] - Benchrest Central Forums

Cabin fever question-when does the case neck expand? -Upon powder ignition, does the case neck expand then release the bullet.. -or does the pressure of ignition of the powder push the bullet out then the some 50KPSI expand the case neck? Bringing up the question is it more important...

benchrest.com

 

[Alex Wheeler]

I'll give you the best piece of knowledge I have about neck tension. It doesnt change the tune. That means its the easiest thing to test. Its not like a primer which will change your powder charge. You can literally shoot your best load with different bushings and pick the best one. Its too easy to not test this. And if your super lazy, do .002 vs .005.

 

[Mulligan]

Not taking a side further but this was a good conversation. MKS in this thread is a sharp guy. Haven't spoken to him in a few years now but I believe he was a mechanical engineer but he was/is a professor at the University of Louisville. He may be retired now. He does bring a scientific approach to how he feels neck tension works, fwiw. It's not terribly long. Good read, still different opinions though.

When does the case neck expand? [Archive] - Benchrest Central Forums

Cabin fever question-when does the case neck expand? -Upon powder ignition, does the case neck expand then release the bullet.. -or does the pressure of ignition of the powder push the bullet out then the some 50KPSI expand the case neck? Bringing up the question is it more important...

benchrest.com

This is a fantastic read with some heavy hitters weighing in on the subject.
Thanks for sharing
CW

 

[Bill Norris]

In the 6mm, most are in the lands. Theres two windows, .005-.008 in or so and .018-.024 in. Depending on what the barrel likes, and the bullet. Testing at 1k, the neck bushing size is night and day. Even just .001 either way. Probably the most overlooked thing in our game. In the .30s more guys do jump, but still theres a spot around .015 in they like too. And same thing, it matters big. I think it has to be tested at 1k if thats your game. I have tuned rifles at 600 that shot tiny but would not group at 1k until I changed the bushing size. I think it matters more the farther out you go.

So with the testing mentioned going from 600 to 1000 yds. did the longer ranges require more neck tension or less ?

 

[Alex Wheeler]

So with the testing mentioned going from 600 to 1000 yds. did the longer ranges require more neck tension or less ?

More

 

[243winxb]

Neck turning = less variations in neck tension. The 223 needs the donut removed, if the bullet shank is seated that deep.

 

[chkunz]

This is interesting
CW

This is a great example of what I am looking for; someone designed a test, ran the test, did data analysis and reported the results. Also, he measured velocity in addition to accuracy which may prove to be helpful in understanding the results. He was very through in defining the process and equipment used in the test. I really appreciate having the benefit of this effort.

If I were to run this test, I would shoot several ten shot groups for accuracy at each of the data points that he presents. Based on my experience with data analysis, one seven shot group at each data point will not give an adequate confidence level for the effect of neck tension on accuracy we are looking. I understand statistical analysis well enough to be guided by it but not enough to teach it. Maybe someone with the knowledge and teaching skills can comment on the number of rounds and groups needed for a reasonable statistical confidence level.

Also, I would calculate mean radius for each group in addition to extreme spread. Mean radius values every point in the group equally while extreme spread only values the two widest points.

Again, thanks for the reply.
Best wishes.

 

[rotts4u]

Sorry...neck tension is the FIRST thing I attend to.

If Danny Biggs tells you its important you better listen

 

[D-4297]

View attachment 1357137

Don't know what discipline you are shooting , but most every F-Class shooter I know takes the subject of Neck Tension very seriously , since most also "jump" our bullets , from as little as .005 to what-ever works in "THAT" barrel . Powder load to group , Seating Depth , and Neck Tension . But most F-shooters start with .001 - .002 .

 

[JFrank]

Looking forward to learning more from this thread. Besides correcting a gross problem with annealing, I've done nothing to evaluate improvements with neck tension.

Here’s a before and after bushing adjustments, not just smaller but far more consistent.

 

[Mulligan]

Here’s a before and after bushing adjustments, not just smaller but far more consistent.

Nice work Jim

CW

 

[gunsandgunsmithing]

Here’s a before and after bushing adjustments, not just smaller but far more consistent.

Nice! I'll say this, not that it's directed at you or anyone in particular, or that it's limited to neck tension, but a couple of those groups show stair stepping up and to the right(or down and left). I think it's worth noting that this is not typical of wind, at least not from a rh twist bbl. I suppose it could be some crazy condition like wind from a roof top or swirling around a building or something similar. It can be mirage or gun handling, maybe even rest setup..but when I see groups form diagonally in that direction, I immediately go to tune. I just thought I'd throw that out there as you don't see it mentioned often and it's just a physics thing. I try to agree with physics when I can. That's all I got. I just think we drift away from basics like that at times.

 

[JFrank]

I’m terrible at reading conditions and always trying to understand tuning but that got me close enough to concentrate on other areas.

 

[gunsandgunsmithing]

I’m terrible at reading conditions and always trying to understand tuning but that got me close enough to concentrate on other areas.

I can see that. Just keep in mind that up and right groups are typically
NOT wind induced. You might have more left in that tube but that really wasn't the point of my post. Some people may not realize what I posted or just not think about it much when tuning. It's one of the first things I look for. I know I'm pretty far out if I get that, believe it or not. IME, that's like .5-.6gr of n133 in a ppc or 2 marks on my tuner. Doesn't sound like much tuner movement but it's typically a max of 4-5 marks from completely in tune to as bad as I can make it shoot. That's all. This is a different subject but up and right is not typically wind. That's my point. Nothing more.

 

[JFrank]

Mike, I think we have talked about that before where no single point of wind takes a right hand twist high right or low left.
When I’m testing I really don’t try and correct for wind , rather make a note of the conditions to help understand the rounds went flat or vertical or just plain weird.
Wish you lived closer I could learn a ton from you.