Elastic limit of case necks ?

@414gates @414gates 2 years ago

I'm wanting to increase the neck tension of my target loads.

I've got as good results as I'm able to get thus far, both with the loads and my shooting, the only thing besides practice is increasing the neck tension.

In my case, I use moly coated monolithics. Monos are 1 thou under jacketed, so you lose 1 thou neck tension there. The moly coat also accounts for something.

I want to bring the neck tension down, and thus the question :

To which point does the case neck remain elastic, before the bullet just stretches it to the final diameter ?

For example, if I size the case without the expander ball, the neck is at it's minimum size. Seating a bullet will stretch the case neck open, to the point where the remaining elastic deformation is gripping the bullet.

[ I'm referring to monolithics here, so the case neck cannot deform the bullet. ]

If I size the neck to where the "neck tension" is 10 thou, and seat a bullet, the seating of the bullet pushes the neck diameter past it's elastic limit, so the remaining amount of tension on the bullet at 10 thou neck tension may be the same as 5 thou.

In other words, there is a limit to how many thou of neck tension can actually hold the bullet elastically.

What is that elastic limit ?

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@T @tripodmvr

https://www.bing.com/ck/a?!&&p=5f500add2be11fe1JmltdHM9MTcxOTk2NDgwMCZpZ3VpZD0yNjAwMGM1NS0zYzYxLTZiNzEtMzJmYy0xZmEzM2Q5YzZhNjkmaW5zaWQ9NTc3MA&ptn=3&ver=2&hsh=3&fclid=26000c55-3c61-6b71-32fc-1fa33d9c6a69&psq=modulus+of+elasticity+of+copper&u=a1aHR0cHM6Ly9tYXRlcmlhbC1wcm9wZXJ0aWVzLm9yZy9Db3BwZXItbWVjaGFuaWNhbC1wcm9wZXJ0aWVzLXN0cmVuZ3RoLWhhcmRuZXNzLWNyeXN0YWwtc3RydWN0dXJlLw&ntb=1

I think a practical test might give some answers. Measure the inner and outer dimensions of the case mouth after it has been through the die without the expander ball. Seat a bullet and then pull it again. You would have to be careful to pull it straight so as to not get it out of roundness. Take measurements again and that should show you what spring back has occurred and what tension was actually applied.

@T @tripodmvr

Very interesting. The light or no neck tension mentioned in benchrest reminded me of a story I read many moons ago. The shooter did not reload beforehand, but had a tub of propellant from which he filled the cases level with the neck, pushed in the bullet and then chambered the cartridge. The bullet seated against the lands and ensured almost identical COL. This method can only be used with an appropriate propellant that will not cause overpressure.

With a single shot rifle used for target shooting a light neck tension can thus be used, but more robust loading out of a magazine and for hunting the grip must be stronger to ensure that the bullet stays in place.

@414gates @414gates OP

Seat a bullet and then pull it again. You would have to be careful to pull it straight so as to not get it out of roundness. Take measurements again and that should show you what spring back has occurred and what tension was actually applied.

Is this not the same as pulling the expander ball through the die, or using an expander mandrel ?

Using annealed brass, I get 0.001" springback in both cases. I've not seen more springback than that [ with annealed brass ] in .243 to 12.7x99 .

I'm not sure that it means the case neck has only 0.001" elasticity in it before plastic deformation.

If so, then there is no practical benefit, or more "grip" involved for more than 0.001" neck tension ?

Unless non-annealed brass has greater springback, in which case more neck tension could apply ?

[deleted]

My mom is a jeweller and I worked with brass quite a lot. I hope this helps:

Brass softens from heating, and hardens a tiny bit every time one works with it. Maybe it is more understandable to say that it hardens every time it bends. In practical terms: filing has a smaller effect than hammering.

This means that every reloading sequence where something moves the material of case neck, it hardens. It hardens less with smaller movements, and more with larger/heavier movements.

I do not yet understand how and why the brass hardens from firing, because it is heated quite a bit, but it hardens nonetheless. I assume that the heating sequence is too short to have a softening effect.

In terms of the expander ball moving through the neck vs a bullet being fired from the neck I do not have good insight. I cannot say how much each procedure influences the brass. Maybe this suggestion can help: take a few batches of cases and reload them three times each, but anneal them at different intervals. One batch completely unannealed, one batch annealed every time, and maybe one batch annealed on the second reload.

Measure all the cases every time.

It should give an idea how much the annealing influences the setback of the brass.

@414gates @414gates OP

Interesting read :

Neck Tension - Lessons Learned

This indicates that per caliber, neck thickness and brass hardness, there is a point beyond with the necks actually lose the elastic tension, and undergo plastic deformation.

@O @oafpatroll

Interesting read :

Neck Tension - Lessons Learned

This indicates that per caliber, neck thickness and brass hardness, there is a point beyond with the necks actually lose the elastic tension, and undergo plastic deformation.

I'd expect that the specific alloy would also be a variable.