Cartridge Neck Tension

[17remhunter]

You guys that are experienced reloaders how important is neck tension . If your using bushing neck dies what do you want How much tension? Does tension have an affect on pressure and could it play a part in load development for accuracy?

 

[Rick Richard]

Lots of folks including me believe the key to accuracy is consistency. So, if we believe that than one part of that equation has to be neck tension. I would suggest experimenting with the .002 to .003 under loaded cartridge brass /neck diameter to begin with.

 

[MagnumManiac]

Well, the actual neck tension (interference fit) is important, the amount it actually is between cases is far more important than the number used.
I used to use a die with a gauge to measure seating force, if that number was more or less than desired in poundage, then the necks were sized more or less to suit. It must be understood that the neck yields first during ignition, so the tension is only doing it's job until .0001" of expansion takes place.


Then, I discovered this number meant little, as I got far better results running .001"-.0015" total tension (interference fit) with spring back reduced into the equation.
Annealing provides me with the least tension I can get away with. As I don't feed from a mag or have rounds in the mag, it is of little concern to me in my comp ELR rifles.
Even my hunting rigs get no more than .002" tension, I've never had an issue with this, even in heavy recoiling cartridges.

Cheers.

 

[17remhunter]

Well, the actual neck tension (interference fit) is important, the amount it actually is between cases is far more important than the number used.
I used to use a die with a gauge to measure seating force, if that number was more or less than desired in poundage, then the necks were sized more or less to suit. It must be understood that the neck yields first during ignition, so the tension is only doing it's job until .0001" of expansion takes place.


Then, I discovered this number meant little, as I got far better results running .001"-.0015" total tension (interference fit) with spring back reduced into the equation.
Annealing provides me with the least tension I can get away with. As I don't feed from a mag or have rounds in the mag, it is of little concern to me in my comp ELR rifles.
Even my hunting rigs get no more than .002" tension, I've never had an issue with this, even in heavy recoiling cartridges.

Cheers.

What you said was very enlightening and informative. Thanks

 

[Tiny Tim]

I tend to undersized a little more than desired and set final interference fit with a mandrel. This pushes any irregularities to the outside and also sets the hoop tension stresses to tighten tension if any of the stress is relieved over time. The theory is that the stress induced in the last operation is reversed if relieved, meaning that when expanding is the last step, any stress induced will result in a tighter grip if released over time. Theoretically.

 

[Rob01]

I size .002" under for standard short action, .003" for magnums and semi autos. Been using those numbers for decades and never had to adjust off them, you should watch using two little as you can get bullets moving under recoil.

 

[Clem Bronkoski]

I just started using bushing dies and I found that .002" good for the 6.5CM but .003" for the 300WinMag. I'm suspecting this is due to its shorter neck.

 

[Rob01]

Magnums like a little more neck tension so you don't get bullet movement under recoil.

 

[WapitiBob]

I use .004.

 

[MagnumManiac]

I tend to undersized a little more than desired and set final interference fit with a mandrel. This pushes any irregularities to the outside and also sets the hoop tension stresses to tighten tension if any of the stress is relieved over time. The theory is that the stress induced in the last operation is reversed if relieved, meaning that when expanding is the last step, any stress induced will result in a tighter grip if released over time. Theoretically.

Hoop strength is only governed by alloy content and ductility, not by the way it is sized.or the size of the hole made. Normalising hoop strength is the goal, sizing length of neck is also key.
If it takes .002" with x brass and .003" with y brass, it is the ductility or alloy making the change. Hoop strength is not ending, it does not increase due to what you do to the brass, it gets less the softer the brass is, but, when brass is over hardened, spring back is nil to the point that the brass hardly has any give. It's ductility is severely reduced. This condition provides very poor neck tension.
Work hardening is a thing we can only change by annealing, without it, inconsistencies are the norm, not the exception.

Cheers.

 

[MarkInPA]

Magnum, what do you think is the best way to achieve consistent neck interference fit? I'm sure annealing is part of the equation. If your goal is to have .002" neck interference, what things do you need to do to make sure each and every case has .002" of interference fit.

 

[Walker375]

Well, the actual neck tension (interference fit) is important, the amount it actually is between cases is far more important than the number used.
I used to use a die with a gauge to measure seating force, if that number was more or less than desired in poundage, then the necks were sized more or less to suit. It must be understood that the neck yields first during ignition, so the tension is only doing it's job until .0001" of expansion takes place.


Then, I discovered this number meant little, as I got far better results running .001"-.0015" total tension (interference fit) with spring back reduced into the equation.
Annealing provides me with the least tension I can get away with. As I don't feed from a mag or have rounds in the mag, it is of little concern to me in my comp ELR rifles.
Even my hunting rigs get no more than .002" tension, I've never had an issue with this, even in heavy recoiling cartridges.

Cheers.

I second this. Aim for .0015 in everything with a max of .002 and a minimum of .001".

 

[Walker375]

Magnum, what do you think is the best way to achieve consistent neck interference fit? I'm sure annealing is part of the equation. If your goal is to have .002" neck interference, what things do you need to do to make sure each and every case has .002" of interference fit.

I anneal ADG brass ever other firing usually. Sizing with a smaller bushing if using a bushing die and then use the correct size expander mandrel to achieve the best fit. A mandrel will give you better consistency because case neck thickness doesn't matter as much as it does using solely a bushing for neck tension.

 

[Walker375]

Magnums like a little more neck tension so you don't get bullet movement under recoil.

I've never had a bullet move under recoil with a 338-378Wby and a 300gr bullet using 1.5- 2k neck tension