Measure neck tension

[chopit]

I am using a lee collet die in my forster co ax. How do i correctly measure the neck tension?OD of bullet -.002 then id of neck or OD of loaded prime round neck .291 (prime brass 130 berger) and adjust die till neck OD is .289? This is for a bolt gun.

 

[chopit]

Or do i have this all wrong and all i will ever get is .001 of the mandrel. When i dial the die down am i just shortening or bulging the case. Bullets seem too loose. Should i get the .002 mandrel?

 

[nexusfire]

Good place to start is neck thickness. Measure the thickness and double it, add to bullet diameter and subtract desired neck tension. Example: neck thickness is 0.015. 0.015+0.015+0.264= 0.294. 0.294-0.002=0.292 bushing.

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[nexusfire]

Idea is to size it down enough that when you run it thru the expander ball or mandrel you are not over working the brass

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[918v]

Lee makes undersized and oversized mandrels. I dunno what you're loading for but here is how it works in .30 cal:

The standard mandrel is .3055". It produces less than 60PSI of seating pressure when used on unannealed necks. It is fine for loads where you jam into the lands, but too light if you're jumping. The reason is ES. Low seating pressure produces high ES. If you jam into the lands, the rifling leade does the job of neck tension.

I also have .3050", .3040", and .3030" mandrels. I use the .304" and .303" mandrels on unannealed necks depending on neck hardness, neck wall thickness, and neck length as these variables affect seating pressure just like neck tension does.

So get some undersized mandrels from Lee. They're cheap.

 

[ZiaHunter]

Get a arbor set up and a force gauge like Km or 21st century... .02 or whatever is just bs .


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Exactly. The only way to properly measure actual neck tension is with an arbor press such as 21st Century Hydraulic or the K&M using chamber seating dies.