How much crimp on 9mm Luger?

NavyNukeET

New Member
I shot my very first ever batch of reloads yesterday. They consisted of 124 gn RMR plated bullets, once fired brass, Winchester small primers, 4.2 gn of WSF, and 1.147 COL. No issues with shooting them, but I was pretty nervous for the first couple of shots :lol: .

My question is regarding the amount of crimp necessary to have on a 9mm case. How do I know if I'm crimping enough/too much? What are the possible dangers of over/under-crimping?

Thanks!
 

biganimal

Member
I only put enough crimp to hold the bullet which is very little
The leading edge of the case is what determines headspace so too much crimp screws up the headspace
 

11B3XCIB

Member
You don't crimp to hold the bullet. You crimp to take the bell or flare out of the case. Neck tension from sizing holds the bullet in.

Danger of under crimping: you don't remove the flare and the round won't chamber.

Over crimping: you press the case into the bullet and it chews the jacketing or plating up.
 

Tigerstripe

Active Member
did you know 9mm is not a straight wall case. it is tapered, as in the size at the base is larger than the size at the mouth?
 

NavyNukeET

New Member
11B3XCIB said:
You don't crimp to hold the bullet. You crimp to take the bell or flare out of the case. Neck tension from sizing holds the bullet in.

Danger of under crimping: you don't remove the flare and the round won't chamber.

Over crimping: you press the case into the bullet and it chews the jacketing or plating up.
So after the case gets sized, the mouth gets flared, then the bullet gets seated to the correct depth. You're saying that the case/bullet interference is enough to hold the bullet?
 

mark_b

Member
When you seat the bullet in the third die, it also removes the flare that you put on the case in the previous die. Depending on how far you screw the die into the press determines how much of the flare you remove. Since it is not a crimping die, it will never roll a crimp on a case like a crimp die (38 special/357 magnum for example) will in the bullet cannelure.

You can either measure the diameter of the case with a caliper or use the barrel of your pistol to see if you have removed enough of the crimp. This is all you need to keep the bullet in position.
 

Tigerstripe

Active Member
i think the 3rd die is a roll crimp die.

put an empty case up the die till it stops, turn in the die 1/4 turn and you have a crimp.
 

11B3XCIB

Member
NavyNukeET said:
11B3XCIB said:
You don't crimp to hold the bullet. You crimp to take the bell or flare out of the case. Neck tension from sizing holds the bullet in.

Danger of under crimping: you don't remove the flare and the round won't chamber.

Over crimping: you press the case into the bullet and it chews the jacketing or plating up.
So after the case gets sized, the mouth gets flared, then the bullet gets seated to the correct depth. You're saying that the case/bullet interference is enough to hold the bullet?
Correct, if the steps leading up to seating and taper crimping have been done correctly (assuming you're shooting semi-auto, not revolver). The tension comes from the bullet being slightly larger than the opening of the casing and getting stuffed down in the brass casing with enormous pressure, which is why you flare the casing: to allow the bullet to rest in the casing for seating. If you don't bell it and just try to balance it on there, you'll probably get an offset round or a crushed case.

A roll crimp is needed in revolvers in most cases because headspacing doesn't occur on the mouth of the case and requires a bullet with a groove or cannelure.

I have this die set for 9mm (and also the .45 ACP equivalent):
http://www.midwayusa.com/product/757170/rcbs-carbide-3-die-set-with-taper-crimp-9mm-luger

The first die decaps and sizes the brass. 2nd die bells/flares the mouth of the case, and the 3rd seats the bullet and, if you choose, will taper crimp (remove the flare from step 2). If you crimp too much, you can run into pressure problems and jacketing/plating getting torn up.

You should not be taper crimping to hold the bullet in place.
 
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