Originally Posted By: big37dogOn the original topic
will new brass expand to the dimensions of the guns chamber on a single firing or would it be wise to neck size a number of times to make sure the cartridge is the size of the chamber before you bump it. ?
Normally, the first time fired brass will not fully fill the chamber - you will have 0.003" to 0.004" of head space and the body will also have about 0.002" thou of total clearance.
If it is a good bolt gun with fully contacting lugs on both sides, you will probably never get to the point where there is difficulty closing the bolt, because there is always a tiny bit of spring back, and with solid lock-up, the brass can only expand just so much.
But if the action doesn't lock up tightly, or only one lug has full contact, then the case might get to the point of being minus 1 thou headspace, which means that you will have some tightness in the final stage of lock-up.
When setting a FL die, you want to size the case the least you can (especially in the shoulder/headspace dimension), and still have the rifle function fully - any more sizing is just wasted case life, because it will lead to head separations.
So, anyway... yes, it is wise to neck-size and fire the case several times to make sure it has filled the chamber as much as it is going to...
... before setting up your FL die.
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