Doesn't the firing pin drive the case forward until it stops against the headspace reference then dent the primer .025" or more to fire the round?
Often, case shoulders are set back a thousandth or more before the round fires.
Full Length or Neck Only; What's Best Resizing for Accuracy?
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Often, case shoulders are set back a thousandth or more before the round fires.
okie man
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How much does a case expand when fired but before the bullet starts moving down the bore? Does it fill the chamber at all? How much does the case fit matter if the case fills the chamber , self centering in the chamber, before bullet release?
Rich Coyle
Well-Known Member
Some have done better with neck sizing. Others no difference.
A 30 caliber cartridge whose bullet needs 10 pounds of push force to start it moving forward in the case neck needs about 130 psi in the case to start with. Bullet cross section area is about 1/13th square inch, force on bullet = 1/13th of 130 psi. Not near enough to fully expand the case to chamber limits.
As soon as the bullet starts into the rifling, several dozen pounds of force are needed to fully engrave the bullet. That's several hundred psi.
In my 308 Win tests, powder charges 15% or more less than maximum ended up with case headspace .002" to .007" less after firing. Primers were backed out about that much past flush with case heads. Shoulders were set back that far from firing pin impact. Case was smaller than chamber.
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Usually your blunger style ejector already has the case pushes forward to the chamber shoulder unless you have a mechanical blade style ejector.
We used to remove the plunger from our single shot target rifles, and pick the fired case out of the action. The theory was that with one side of the rim held back by the extractor, and the opposite side pushed forward by the plunger, if there was any slop the cartridge would be held at an angle to the bore.
Not sure if it made any difference because most of us were neck sizing, but it did make it easier to keep control of your brass.
I guess this is pretty irrelevant in a hunting situation though.
fiftybmg
Well-Known Member
Concentricity of a loaded round is a product of the seating die.
Regarding bore alignment, the chamber tolerance automatically disqualifies the bullet from true bore alignment, because gravity will cause the round to sit at the bottom of the chamber, and the bore alignment of the loaded round is then [chamber tolerance / 2] out.
Regarding bore alignment, the chamber tolerance automatically disqualifies the bullet from true bore alignment, because gravity will cause the round to sit at the bottom of the chamber, and the bore alignment of the loaded round is then [chamber tolerance / 2] out.
Several people have proved bullet seaters align bullets to the case neck axis. There is a couple thousandths clearance from the seater die to bullet and case neck. Little, if any, neck straightening happens.
If you've ever watched a bottleneck case neck position in the chamber neck, you'll notice it centers perfectly from ejector and firing pin force raising the case body off the chamber bottom when in the firing position with the case shoulder well centered in the chamber shoulder aligning the case neck in the chamber neck center. If case headspace is .002" less than chamber headspace, there probably isn't enough room for the case body to touch the chamber bottom anyway; case won't slide back far enough.
You'll first need to cut the barrel off at the chamber mouth. This decades old myth is easily dismissed.
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I have had good results using both approaches. It really depends on the particular chamber and load. In recent years, just about all my precision competition and LRH loads are FL sized....for many of the reasons mentioned. Sometimes when doing load development, or barrel break-in I'll neck size just for expediency. LOL, back in the late 60's/early 70's my first reloading was done with a $4.99 Lee a Loader Kit for my 30-06. It neck-sized by hammering the case into the dye. Groups were still half the size of factory ammo...and, at a fraction of the cost!
jepp2
Member
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Backcountry sports
Well-Known Member
If you are getting great groups now, I wouldn't bother with neck turning. Lots of competition guys are going to no-turn chambers, with great results.
Blacktailer
Well-Known Member
The problem with standard neck size dies is that the cartridge body is typically not supported as the neck is sized and can therefor induce run out. I had a neck size die that induced 6-7 thou run out in sized cases. That is why for neck sizing I either partial full length size or use a collet neck sizer.
Shadowwalker
Well-Known Member
Smart man!
