NK vs FL resize

[Salavee]

Originally Posted by elkhunter11

I would agree that the first firing should see the greatest increase, but I am still wondering if the case fully forms to the chamber on the first firing, and simply springs back less with each successive firing, as the case work hardens. So the volume while firing may not actually increase with each firing. Since we can't measure the case dimensions at maximum pressure, we will never know.

I see no reason that a case wouldn't fully form on the first firing. At 50-60,000psi, how could it not ? The case expansion will be greater on the first firing with the amount of case expansion remaining fairly constant after that, at least constant enough to be barely discernible. Other than a minor increase in case capacity with a neck-sized case I have found very little, if any, difference in velocity or accuracy with either method of re-sizing. Normal velocity spreads are usually greater, so it's hard to tell if the case sizing method is causing the differences.

[Ryan.M.Anderson]

Originally Posted by chuck

This would also be an exceptional way to size cases. How do you determine mandrel size?

There is a place in the US that sells expander and turning mandrels. I can't remember off the top of my head which size is which but one is .001 under and the other is .002 under.

I just use the expander mandrel and let the tension be what the tension will be. I guess more handy folks could get custom ones sized or make ones.

This method has produced many accurate loads for me and I think (personally) that it keeps the shoulders more accurate (the expander button isn't pulling on anything).

[Salavee]

Originally Posted by Ryan.M.Anderson

There is a place in the US that sells expander and turning mandrels. I can't remember off the top of my head which size is which but one is .001 under and the other is .002 under.

I just use the expander mandrel and let the tension be what the tension will be. I guess more handy folks could get custom ones sized or make ones.

This method has produced many accurate loads for me and I think (personally) that it keeps the shoulders more accurate (the expander button isn't pulling on anything).

Check out the Lee collett dies. They do a great job and are relatively inexpensive/

[lclund1946]

Originally Posted by chuck

That is standard practice. I assume it is because you have a bullet in the neck to varying degrees and therefore to have some semblance of consistency they do that.

That may be standard practice for you but the object of measuring case capacity is to determine how much H20, or ultimately how much of the powder that you are using, fits under the bullet before being compressed. Most Cartridge design programs, at least the one I use, have drawings of Sammi Maximum Cartridge cases that give the average H20 capacity. It also has the capability to draw the seated bullet, of course you have to have accurate measurements, at whatever depth you want and determine the H20 Capacity W/Bullet. Then you use the formula, H2O Capacity W/Bullet/ H20 Case Capacity = X/Powder Case Capacity. X gives you the Powder capacity under the bullet.

[Ryan.M.Anderson]

Originally Posted by Salavee

Check out the Lee collett dies. They do a great job and are relatively inexpensive/

The lee collet dies would not work very well for what we are doing.

I guess if you combined them with a shoulder bump die they could be ok but then I am doing 2 steps anyways and might as well just use the mandrel.

[260 Rem]

For the purpose of an accurate measurement of the internal volume change between FL/NK sized cases ...I believe using water is the best method that can be used. Adding a bit of dish soap will reduce surface tension and reduce the meniscus (bubble) effect.

[260 Rem]

Originally Posted by Salavee

Check out the Lee collett dies. They do a great job and are relatively inexpensive/

I am sure somebody must have tested this theory, but I would speculate that NK sizing with a collet may result in inconsistent NK tension as the necks become work hardened and lose elasticity? I suppose that could be mitigated through changing mandrel diameter? Or, annealing. What is your observation?

[Salavee]

Originally Posted by 260 Rem

I am sure somebody must have tested this theory, but I would speculate that NK sizing with a collet may result in inconsistent NK tension as the necks become work hardened and lose elasticity? I suppose that could be mitigated through changing mandrel diameter? Or, annealing. What is your observation?

The Lee collet dies incorporate a mandrel The mandrel ,as it is supplied, provides a light press bullet fit on a once-fired case neck. It can be polished down to -.001 for a tighter fit if desired. Tighter mandrels are available. Neck concentricity is very uniform and no lubrication is required. In addition, work hardening is substantially reduced when compared to an expander plug. Of course, any work hardened cases should be annealed as required. It is a different system and very inexpensive but it does a very nice job of neck sizing from my experience... It is as accurate and consistent as a bushing and only about $40.00 for the neck die and bullet seater. It's one of the more innovative products from Lee.