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ShortBus

.374 crimp for 9mm?

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Loading some blue bullets (125's) for production. Been using .377 on my buddies press and the first few bullets I ran on mine crimped at .374. Is that too tight?

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Likely yes. Pull the bullet and see.

Sent from my SM-N920P using Tapatalk

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Yea I need to do that. Should have done that before I made a thread lol

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Crimp is bullet diameter plus .022 ( 2 x case wall thickness) . If your bullet is .355 then the crimp should be .377

Plated or lead bullets are usually .356 which will yield a .378 crimp

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I am running .371 on my 9mm for a G34 and haven't had any issues. With a stock G34 and 124 MG JHP's it shoots 1 ragged hole at 25 yds off the bench.

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Good to know! I'm gonna shoot the ~80 I loaded and see how they do/feel.

Edited by ShortBus

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The equation, crimp diameter = 2x brass thickness + bullet diameter is a good guide to start: For Autoloaders! Revolvers are a whole different animal, even 9mm revolvers.

For autoloaders just remove the flare to ensure no bullet setback (push test) and good feeding (plunk test).

That's the long answer. The short answer is that I usually crimp 9mm pistol (not revolver) ammo to .377 using .355 nominal jacketed bullets. This generally results in best accuracy and no damage to bullet jacket, plating, or coating. You may want to crimp a little tighter with slower powders to get better combustion and bullet pull.

If you are using mixed headstamp brass in a batch, you will want to err on the side of tighter crimp to prevent bullet setback in the brass with thinnest walls.

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There is some disputed info here.

More crimp does not prevent setback in my experience.

Neck tension, or the sized case holds the bullet. In my experience increasing the crimp actually swages the bullet and reduces neck tension resulting in increased possibility of setback.

A good approach is to measure your case wall thickness and add that to a measured bullet diameter to arrive at a crimp that does not swage the bullet.

The best approach is to research this issue beyond forum posts, good luck amigo.

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.374 is tight.

the thinnest 9mm case walls I have seen and measured is .010.

if your bullets are 9mm they are .355 and so you are over crimping.

now for the truth of this... your bullets could be small, your cases thin, and .374 is the correct crimp.

you may find some pistols do not like your ammo....

how is the ammo shooting?

miranda

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If it works, don't change anything. If it doesn't, fix the problem.

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I used to do the measure the bullet and case wall thing until a gunsmith asked why I was going through all that trouble. Measure the with of a loaded round right behind the crimp. Subtract .02 and you should be fine. Haven't had a problem with this method at all using JHPs and Bayous. Agree with Ultimo. Crimp does not impact setback. Neck tension does and too much crimp can negatively impact that.

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oh because I can post.....

Hi neomet,

subtract 2 thousands?

ya know some people ask the strangest questions and I have to think about why

they ask and and often guess what the are looking for.

this was one of those questions.

I expect most 9mm pistols will run ammo crimped at .370

buuuut I don't think that is a good idea.

I do agree with you that what the 'smith said has merit.

I measure bullets and case walls so that I know when I am assembling the ammo,

I'll know if I may be creating problems.... neck tension is certainly one possible problem.

if you want ammo from mixed brass and have few worries about the result

you would want jacketed bullets, a tight sizing die, and to set the crimp at .378

miranda

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Haven't pulled a bullet yet but did shoot 80 rounds of the .374 yesterday and had zero issues.

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On 5/23/2016 at 12:21 PM, ShortBus said:

Loading some blue bullets (125's) for production. Been using .377 on my buddies press and the first few bullets I ran on mine crimped at .374. Is that too tight?

I think factory recommendations is .380

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On 5/25/2016 at 7:19 AM, ShortBus said:

 did shoot 80 rounds of the .374 yesterday and had zero issues.

 

As long as it feeds and is accurate, it's GTG.     :) 

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SAAMI Spec is 0.380 I believe. I go ~0.378 basically as little as i can while still holding projectile firm.

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4 hours ago, ringram said:

 I go as little as i can while still holding projectile firm.

 

The crimp, in a semi-auto, doesn't "hold the bullet firm".

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To my knowledge crimp just ensures the round will feed? So if it passes the plunk test, it's good to go.

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Posted (edited)
On 5/24/2016 at 7:36 PM, practical_man said:

If you are using mixed headstamp brass in a batch, you will want to err on the side of tighter crimp to prevent bullet setback in the brass with thinnest walls.

 

Never had any luck playing with crimp to try and prevent lead from setting back or walking out.

 

For a 929 revolver (if lead is going to walk out this is the gun to find out with, Walmart Federal 115's will sometimes walk fully out of the brass by the time you get to round eight ) and my semi autos my crimp pretty much just takes the bell out of the case and brings it flat to rest against the bullet. 

 

If you crimp too much on coated you will start to see groups really spread past 20 yards or so, it is a bit like throwing a late breaking curve ball. 

Edited by IHAVEGAS

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Revolver bullets typically have a cannalure which allows for use of a roll crimp, the combination of which prevents bullet setback due to recoil.  Semiauto cartridges have a taper crimp, which facilitates feeding.  It does not, and is not intended to, prevent bullet setback (whether due to feeding, recoil, etc.).  That's accomplished by using a sufficiently sized case which creates an interference fit.  If the case isn't sized correctly, adding more crimp will not prevent setback.  Adding too much crimp will negatively affect accuracy.

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On ‎5‎/‎25‎/‎2016 at 7:19 AM, ShortBus said:

Haven't pulled a bullet yet but did shoot 80 rounds of the .374 yesterday and had zero issues.

If it ain't broke, why fix it?😀

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Posted (edited)

Function and accuracy are two different things. Your rounds may have functioned but over-crimping can sometimes create poor accuracy. I see no reason to crimp 9mm to anything tighter than .377ish.

Edited by 4n2t0

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On 5/24/2016 at 5:36 PM, practical_man said:

You may want to crimp a little tighter with slower powders to get better combustion and bullet pull.

If you are using mixed headstamp brass in a batch, you will want to err on the side of tighter crimp to prevent bullet setback in the brass with thinnest walls.

 

Nope to both of those sentences. Crimp does very little to affect combustion or bullet pull in semi-autos, and if you are relying on crimp to prevent setback, you need to improve case neck tension. 

 

As a general rule in 9mm, just enough "crimp" to remove the case flare (leaving the case straight) is plenty. Done right, that doesn't apply a crimp at all. This gives best results for coated, wax lubed cast, and plated bullets, and works just as well with jacketed. Most jacketed bullets can tolerate a lot more crimp, but it's unnecessary if the case is sized right and has adequate neck tension. The wasp waist in a loaded round between the bullet and case head does far more to prevent setback than a crimp does. 

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