Will neck sizing change velocities.

Discussion in 'Reloading' started by land308, Feb 9, 2010.

  1. land308

    land308 Well-Known Member

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    I am just starting to neck size brass for my 308 win to get better brass life and not have to lube cases. I have read that after a few firings I may have to full length size to ease chambering. Will there be significant velocity differences between the full length sized and neck sized brass due to case volume differences? On average, After how many firing do you have full length resize. I am using the lee collet die.
     
  2. Winchester 69

    Winchester 69 Well-Known Member

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    It depends on how closely your FL sizing die replicates your rifle's chamber. If the sizing process alters the case's capacity, higher pressure will result. If the case is minimally influenced, pressure won't be affected.
     
  3. Winchester 69

    Winchester 69 Well-Known Member

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    Post deleted.
     
  4. Bart B

    Bart B Well-Known Member

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    Any case sizing method will produce the same peak pressure and muzzle velocityfor a given case as long as neck tension's the same. Note that at peak pressure, the case is pressed hard against the chamber walls. The same case will always have the same volumn at this time regardless of how much it had after sizing it before it was loaded and fired.

    Folks have got dozens of reloads per .308 Win. case full length sizing them the proper way. And best accuracy, too. Sierra Bullets full length sizes their cases used to test their bullets for accuracy shooting them in standard SAAMI chambers. Many benchresters are moving to full length sized cases these days.

    People used to lap the necks of standard full length sizing dies out to about 2 thousandths less than loaded round diameter and set the fired case shoulder back no more than 2 thousandths. Deprime fired cases first with a die that doesn't size the fired case, then clean them; tumble, vibrate, ultrasonic. Remove the decapping pin and expander ball from the lapped out die then set it in the press such that fired case shoulders are set back 2 thousandths.

    RCBS and Redding make full length bushing dies that do the same thing. Use a bushing of the correct diameter.
     
  5. land308

    land308 Well-Known Member

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    Thanks for the replies. It makes sense that the brass is just going to stretch to the chamber size so things shouldn't change much as far a pressure.