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Neck tension and pressure velocity

Loading 350 rem mag. Lee dies giving about .001 neck tension which was not enough to keep bullets from pushing into case with very moderate pressure. Tried a Redding die now getting .005. .376 sized brass .381 loaded round. Bullets seated a little harder obviously but not radically so by feel. I did have one case that was .375 or .006 under and seating force was extreme. Pulled that round. Question is how much velocity pressure increase from .001 to .005 neck tension? Running a load with Ramshot Tac that is at the low end of Barnes data.
 
Ok. I was just wondering how much difference since I had worked up a load at .001 with the lee dies. I reduced the powder charge 1/2 grain since 58 and 58 1/2 were what for what.
 
Does your Redding die partial length size? No more length than seated bullet bearing?
I’m not sure I understand where your going with this. I set the die up to not bump the shoulder since the brass had been sized once in the lee dies and the shoulder bumped .002. I backed the die off so it would just size the neck and nit touch the shoulder.
 
I have a 223AI that I have finally gotten around to doing load development. Initially (a year ago), I fired a bunch of factory .223 ammo to fire-form cases to the rifle's chamber. I went to resize these cases through my Redding 223AI Full Length Resizing S Bushing die. There was a lot more resizing of the body then I cared for, and I will send off die to have it honed to my chamber.

The Neck OD of the fired brass was 0.255", which was tight enough for me to hand press/push bullets into case with just enough tension to loosely hold bullet in place. Based on rough measurements, I believe there was .004"-.005" gap between case neck and bullet. The seating depth plus any irregularities/denting along the case mouth was sufficient to hold the bullet, barely. I decided to see what would happen so I loaded (1) 10 rounds of Non-resized cases and (2) 10 rounds of Full Length Resized cases with 0.247" neck bushing.

I assumed that proper neck tension would seal the gases behind the bullet helping propel it down the barrel more effectively/faster. Whereas, the inadequate seal of the non-resized brass most likely allowed some of the gas to escape out around the bullet causing less pressure pushing the bullet. The average velocity was only 25fps faster with the Resized Brass... I thought this would be greater difference.
 

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