Neck Tension for Seating Bullets

338winmag · Jul 12, 2011

Spoke with Lee yesterday and the one tech mentioned that neck tension should be about .001 for such bullets like .308? That seems extremely light. Using the Lee Collet Neck sizing die I am setting die to about .002 to .0025.

Anyone have an exact way to measure or thoughts on the subject.

FOTIS · Jul 12, 2011

You measure the diameter before and after?

338winmag · Jul 12, 2011

I have measured just recently in trying to find out why I have such FPS deviation between shots.

Guy Miner · Jul 12, 2011

Neck tension can play a role in lessening the variation between shots.

One of the reasons I like to use sizing dies with bushings that can be swapped - giving me a lot of control over how tight the neck tension actually is with my loads. Not all of my dies are so equipped, but some are, and they typically produce excellent loads.

FWIW, Guy

rick smith · Jul 12, 2011

Using the Type "S" neck bushing dies from Redding, I measure the neck OD of a loaded round from the brass lot I am using. Then subtract 0.001-0.002 thousants and order those two bushings. In certain calibers I have six or more bushings due to different manufacturers neck thickness.Rick.

atmoshpere · Jul 12, 2011

338winmag":18kk7yon said:
Spoke with Lee yesterday and the one tech mentioned that neck tension should be about .001 for such bullets like .308? That seems extremely light. Using the Lee Collet Neck sizing die I am setting die to about .002 to .0025.

So is he recommending using a mandrel that is .001 smaller than your bullet diameter? Do necks have the same spring back after being sized with the lee collet as they do with other sizers? In other words, once you remove your sized case, do you find that the internal neck diameter is the same as the die mandrel diameter, or is it larger by a thou or two? Guessing it would be larger by a bit or it wouldn't come out very easy :?: To get your 2 to 2.5 thou did you have to order a custom mandrel from lee or did you modify it yourself?

338winmag · Jul 13, 2011

I should have stated in the last post reply that I believe the Lee Tech to be incorrect. When I apply 20-25 pounds of pressure, I get between .002 and .003.

atmoshpere · Jul 15, 2011

I was under the impression (quite possibly false :? ) that the madrel diameter controlled the amount of neck tension produced by the Lee die by controlling the internal diameter of the neck as it is pressed against the mandrel by the collet. With this setup, would your neck tension change with increasing pressure applied to the ram lever, or does it simply transfer that pressure to the die cap after the neck has been fully pressed against the mandrel? I don't own one of these yet, so I am curious as to how they function and how you can adjust your neck tension with them...