case length

I

IdaSpud

Inactive
Hi all. 45 years ago I used to load 7mm mag but have not done any reloading since. I'm just starting to load again only this time I'm starting with a 9mm load. I am using CFE Pistol powder 5.1 gr to 5.7 gr and 115 gr jacked rn. The cases I used measured .745" to start but after firing they measured .740 - .741". Why would the cases get shorter after firing? My other cases that I did not use were longer to start. .748 - .752. I seated to col 1.130.
Thanks for your imput.
 
That's because when the round is fired, the case expands, increasing the diameter to fill the chamber, which in turn shortens the length. Now when you size the case it should return to its original length, possibly longer.
 
9mm is a slightly tapered cartridge, subtle but there.

As long as the case round is within the book limits, you are fine.

COAL is a different issue, book is usually good but taking a gun apart and dropping a round into the chamber is a good way to confirm.

Generally pistol case don't grow like rifle cases.
 
Thanks condor bravo, you were right. After resizing, they returned to their original size.
Next question, how do you get an even crimp if the cases are not of the same length? From all the research I've done, nobody pays any attention to case length, they just load and shoot. Seams to me that a light crimp on a case that is .745, without resetting the die, would be a tight crimp on a .751 case. Am I missing something? Or does the crimp pressure not matter?
 
If you crimp you want uniform case length particularly with a roll crimp. Taper crimping in a separate step is a bit more forgiving.
 
The crimp pressure does not add much to the overall bullet tension which is primarily the bullet to case fit, controlled by the sizing die and bullet diameter. For the crimp just apply what appears to be an average taper crimp, rather than roll crimp, for the various length cases. The differences in case lengths will not make that much difference. It would be frustrating to try to trim 9mm cases to all the same length. 9mm's might be difficult to get to your complete satisfaction due partly to the slight case taper.
 
Fired handgun cases get larger in diameter thus shorter.....but when you resize them and make them skinnier ...they get longer again.

Gary
 
I'm a benchrest shooter 308 Cal. Reloading for rifle cases are trimmed to the exact same size , thought I had to do the same for reloading 45ACP auto until the guy's here straightened me out . No trimming pretty simple to reload accurate pistol ammo. . All good advice .

Chris
 
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