9MM crimping question

[Bnowlin48]

I've started loading 124 grain fmj-rn bullets over 3.4 gr of Hod. Tite Group on a Lee Turret press and I'm putting a light crimp on the cases. (not a roll crimp). I've just started shooting an auto loader and I'm concerned that the bullets might get pushed back into the cases and cause a pressure spike. I have always shot revolvers and I know I need a decent crimp to keep the recoil from re-seating the bullet for me. What is your normal crimp (if any) for this sort of application? Am I just being a fussbudget? I have a history with shotgun reloading but not pistol and rifle ammo.

 

[docsleepy]

Adjust lee seater until you see tiniest bit of color change at tip of older case, proving it was smushed slightly.

 

[Walkalong]

Neck tension holds the bullet. All the "crimp" you need is enough taper crimp to remove the belling, or a hair more. I adjust the crimp so the shortest cases get the bell removed completely, and the longer ones get about .001 indention.

Here is a .38 Super. It crimps just the same as other auto calibers like .32, .380, 9MM, .40, .45.

Here's a .45.

 

[rcmodel]

1. A Taper-Crimp DOES NOT hold the bullet in the case like a revolver Roll-Crimp does.

2. Proper case neck tension alone is what keeps the bullet from setting back during feeding.

3. Too much Taper-Crimp can actually make the bullet looser in the case rather then tighter.
Because any excess taper-crimp squishes the soft lead inside the soft copper jacket inside the case.
Then the harder brass case springs back away from it more then the softer bullet springs back when it comes out of the die.

4. Proper 9mm Taper-Crimp die setting is .376", measured at the case mouth of a loaded round.
That is for feeding and chamber headspace, not a tighter bullet fit.

5. Proper die expander dia. should be .350" - .352" or so.
It shouldn't expand the sized case at all.
Only act as a slip-fit guide to keep the belling portion of the expander aligned inside the case.

rc

 

[tightgroup tiger]

I use a light taper crimp only to straighten out the flare and have never had a setback or neck tension problem with any brand of brass I use.

The neck tension comes from the sizing die being screwed down to touch the shell plate so you get a fully resized case and the flaring die set to the minimum so as to just be able to start a bullet.

My taper crimps don't hold anything on my 9mm rounds.

 

[nix4me]

agree with rcmodel. 376 is the right crimp on 9mm as measured by calipers.

 

[edleit]

I've been a fan of the Lee Factory Crimp Die. For my pistol rounds (9mm, .45ACP) I find that this device gives a more consistent result than trying to crimp in the seating die, and is less sensitive to case length variations.

 

[Nordeste]

I checked several factory ammo rounds, from different manufacturers, from Fiocchi and Santa Bárbara NATO spec FMJ, to Remington UMC, Sellier&Bellot, Magtech, etc, and they all measured those .376" at the case mouth that RC advices. In my units, that is 9.55 mms and that is how I set my dies to finish my rounds, they all measure those 9.55 or 9.56 mms and they work OK.

I wonder, however, if I should go easier on the crimp provided that I use copper plated bullets, or leave it be as it is.

 

[Potatohead]

I wonder that sometimes myself.

 

[rcmodel]

I wonder, however, if I should go easier on the crimp provided that I use copper plated bullets, or leave it be as it is.

Pull a bullet and see if the crimp / case mouth is making an impression into the plating.

If it is, It shouldn't be.

rc

 

[Nordeste]

Pull a bullet and see if the crimp / case mouth is making an impression into the plating.

If it is, It shouldn't be.

rc

Yes, sir, there is that small indentation on the bullet. That's why I wondered if I would be crimping too much. You can feel it with your fingernail. It's not excessive, but there it is. My bullets are .356" RN.

I guess the solution is backing off my crimp until I pull the bullet and there is no indention on it , which leads me to the conclusion that the .376" rule is not exact in every case.

Thanks .

 

[rcmodel]

Not if you are using .356" bullets.

That would make it .377"!

It also can vary slightly with different case neck thickness on different brands of brass.

rc

 

[Nordeste]

Not if you are using .356" bullets.

That would make it .377"!

It also can vary slightly with different case neck thickness on different brands of brass.

rc

That's the point. I've measured different brands of brass and there are slight variations, so I adjust my dies accordingly. Add the case thickness (x2)+bullet caliber, then substract .004. In my case, it turns out to be that .377, but I've tried making a few dummies and if I used that crimp, when I pulled the bullet there was that indentation on it. So I backed it off to .378 and loaded fifteen rounds with two different charges and OAL.

Today at noon I was at the range with my loads, pistol, and chrony. The results have been surprising. I've lost like... 5? ft/sec of velocity, but the deviation is smaller and the shot feels nicer. I still have to test it at the bullseye range for accuracy but I have a feeling that it will perform better. I did some Googleing on crimping and accuracy, and on semiauto cartridges, it looks like an excessive crimp will really worsen the pistol's accuracy.

 

[1SOW]

To not impact neck tension, only bell the case the minimum needed to hold the bullet upright. Bullets with the nice rounded edges on the base may not need belling or maybe just a skosh.
With 9mm, setting the taper crimp from .3775" to .3785" will cover all the bases for case variations. Without the math, just start by screwing the die in til contacting the short case. Every two degrees you screw in the die adds .001" to the taper crimp. When it gets to .3785" with a short case , you're good to go for all.

If you use the LEE FCD for taper crimp, the same is true with the taper crimp adjust knob.