more case forming

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  • Last Post 25 October 2018
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Ross Smith posted this 25 October 2018

I made 2 new cases for my 308x1.625 today. I felt I needed to seat the bullet further into the lands and get the driving band further into the throat. After squeezing the cases down i did mydarndest to get them exactly 1.625" long. They fit the chamber with no resistance. I inside reamed the necks to just deep enough to allow the gc to fit in the neck and no further. They have an inside neck shoulder that only allows seating so deep. In essence, they are self breach seating if that makes sense. The cases are loaded at the bench and each was shot 30 times. I checked their length and found they had shortened .004", not stretched. So is this typical of fire forming and if so where does stretching come from, sizing?

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RicinYakima posted this 25 October 2018

Case length lessening is almost always from the case more closely conforming to the chamber walls. As brass expands at peak pressure, it shrinks as the pressure drops. Case lengthening is equally, over stressing the brass so it flows forward with the powder gases, or the die reducing the neck excessively and the expander ball pulling the metal forward when removed from the case. At least that is the standard answer from the reloading companies!

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Ross Smith posted this 25 October 2018

Ya Ric, I expected something to move after making a 30-06 into an 1 5/8" .308.  308 family cases tend to wrinkle around the mouth during forming so 06 is goodr

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