i have a bunch of once fired 9 mm cases.i want to know what the shortest case length ican use should be? the cases are different brands.such as,win. rem. s-b. fed. the case length run anywhere between .740 to .750.i have plans to use from .745 to .750.i am loading ii5gr. plated rn. rainer bullets. i know i cannot crimp too deep.i have a lee factory crimp die.will .005 thoundths variation be too munch? i think the .740 to .745 possiobly too short.i am loading with 5.8 grains of unique. rainier says 5.6 to 6.3b gr. oal. 1.135 all rainier recomendations. any help or opinions appreciated. thanks. scooter-2

Anything between maximum length and trim to length in your reloading manual will be fine. Life's too short to worry about 9mm pistol brass length.

The problem with going too short is the crimps won't be the same. When I reloaded this cartridge I trimmed all cases to .744 long. .754 is max length.

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Little or no crimp is correct with the 9mm luger cartridge. The real purpose of the crimping stage is to remove all case mouth flare from the finished cartridge.

Variations in case length will cause velocity variations, which in turn causes vertical stringing. This is important only for match competition quality reloads.

The minor variations in 9x19mm case length will present no problems in ignition reliability since most 9mm pistols give almost unlimited firing pin protrusion.

The Lee FC die will not over crimp a case.

Screw the knob down on a loaded round until it stops. Then back the case out and turn the knob about 1/2 to 3/4 turn and you are good to go.

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Still Running Against the Wind

I challenge anyone here to shoot their pistol well enough that .005 difference in case length is going to cause a miss instead of a hit. I know I certainly can't.

Make sure all your cases are somewhere within tolerance, and apply a light taper crimp to the final rounds. That's it. I can't imagine a bigger waste of time in reloading than trimming 9mm brass...

The problem with 9mm brass is that it shrinks when you size it, and it does not get longer when you shoot it. I toss mine at .745 I used to shoot mixed case lengths and I got some fairly bad loads. Some just shot wild. After I started tossing the brass at .745 my groups tightened up. I think you are on the right track scooter.

I've got a bunch of Fiocchi 9mm brass that started life at .750", and has "grown" after several firings to .745"... In my experience, auto pistol brass doesn't grow, it gets shorter due to the peening of the case mouth on the end of the chamber.

Personally, I won't worry about the 9mm case length until it gets to .740", or if I start to get malfunctions. It's not clear from your post, so I'll just remind you to always check your case lengths after resizing, not before.

thanks for all the information. i think if i keep my case length between .745 to .750 i won't have any problems. i don't think i should go below .745. i thank you for all the help. scooter-2

I'll quit before I go to trimming 9mm brass.

Sgt Preston here.
I load & shoot several thousand 9mm rounds every year.
My brass is all old mixed head stamps.
I inspect each piece carefully before reloading, particularly for split ends.
I have NEVER measured or trimmed a 9mm case.
Everyone one of my rounds goes bang the first time.
I attribute this to Winchester Primers & WIN 231 Powder.
And every round will travel to the center of the dot if,
I hold on the dot & squeeze the trigger.
I use a light taper crimp & crimp to a dia of .378 / .378,
measured at the end of the brass right next to the bullet.
For the record, I fire all my 9's our of a Springfield Stainless 1911.
Hope this is helpful.
Sgt Preston USMC LLA.

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Except I use 4.5 gr power pistol, and a Kahr PM 9 and a Sig P239

Sgt - I "get" that most people don't trim semi-auto cases. What I don't get is how you can have a consistent "crimp" on different length cases. Since the amount of crimp is determined by the distance that the bullet tavels into the die, a longer case will have a deeper crimp.
I use range brass and have seen a fairly big difference in length, even comparing the same headstamp.

Not to be contrary, but it shrinks in length when you shoot it and gets longer when you size it. (The case expands around the circumference when it's fired and it gets shorter.) I've measured a few before and after sizing and they grow an average of 0.004" after sizing.

I don't know whether they get progressively shorter but I'm guessing they are tossed before most of them are too short.

A friend of mine on another forum did a test using one once fired range pickup 9mm case. The case measured once fired at 0.746" once resized it measured 0.748".

He subsequently fired and resized the same case ten time and recorded the length of both the fired and resized case. Take into account that this case is now being fired in his gun so the original fired and resized case will vary slightly from the old existing case lengths due to chamber dimensions.

On average the fired cases shrank to between 0.744" to 0.743.5" after resizing the same case over ten firings measured 0.749" to 0.748" after resizing.

Two thirds of the time the case when resized measure 0.749" the rest of the time it measured 0.748" to 0.748.5"

Pretty much THIS.

It's the expansion when firing that shortens the case, just as hoses shorten when pressurized. As the case expands outward, it has to shorten. Resizing tends to re-lengthen the case. The working of the brass (expanding - resizing, flaring - crimping) will harden the brass and eventually lead to cracks/splits.

Sgt Preston back again...

My experience has taught me that the 9mm just needs a crimp...

It is imperative that it has some crimp to keep the bullet in place...

With too little crimp, the bullet could be forced deeper into the brass...

by the action & inertia of the gun itself...

This would raise internal pressures perhaps to an unsafe level...

With too much crimp, the accuracy could be affected...

I use a simple test on my ammo to make sure it has enough crimp...

I didn't make this test up, someone taught it to me years ago...

First I measure & record the overall lenght of a finished round...

Then I hold a finished round like it was a pen or pencil...

The primered end faces my face...

The bullet faces end my workbench...

I place my thumb over the primer...

I press down hard (20-30 pounds?) with my thumb...

Finally I re-measure the overall length...

If the round got shorter, I need more crimp...

I use the same test on my 45ACP's & 38's...

It just seems to work for me & my ammo is quite accurate...

I can't see any difference form round to round with the ammo...

I can however see a difference, when I don't hold well or...

squeeze the trigger as well as I'd like...

I call each shot in my mind when the hammer falls...

For example 9 / 10 ring split at 3 O'Clock...

That's typically where the bullet "prints" the target...

Hope this is helpful...

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