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Lucreau

Case crimping too tight?

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So I will say I am a new reloader. I spent the last 8 months with a Dillon xl650 in the box, and doing strict research on the basics, and up to load data for my akai open gun. Last week finally got it all setup on the bench. I’ve got a few hundred dry rounds ran through the machine now, got my powder to where I want it to start on the lower end. The ONLY thing I cannot find much info on is case crimping. I feel my crimp is good, but my question is can it be too good. Can the crimp be too tight, increasing pressures in the load? And if so, what’s a good way to test/tell that my crimp is good to go? Or is there a measuerment range I can take with my calipers of the top of the case? It doesn’t feel like it’s a lot of force in my roller handle when it gets to the crimp die

Edited by Lucreau

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Assemble a round and pull the bullet after you seat and crimp. If there is a ring around the projectile its to much. If there isnt one run it through again with a little more crimp until you get the ring then back a bit at a time off until no ring exists, must use a new projectile. That is your crimp setting.

 

A good place to start is to measure your projectile and the casings wall at the mouth. Double the case wall measurement and add it to the bullet diameter you are loading. That should be your final crimp OD measurement. The final test after you have figured out your crimp is to push the finished round, projectile down, against the bench pretty hard. Measure OAL again to see if it has any set back. If none than you should be good to go. 

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Too little "crimp" and the rounds won't feed (because of the bell in the top of the case);

 

Too much "crimp" and you will lose accuracy - don't worry about more pressure - won't happen.     :) 

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I like .378 but pull the Bullet an make sure your not over crimping 

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Awesome thanks guys! I’ll do the projectile test with the ring, and measuring diameters. 

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There is taper crimp and roll crimp.  They are both crimp.  Taper crimp though, should not take the crimp past flush.  It should take the crimp TO flush.

Crimp should be .380 or less, per 9mm spec. 

.376/.377 is common for .355 bullets, and .377/.378 is common for .356 bullets.  There is no advantage to crimping more the necessary, and the penalty for crimping more than necessary is damage to the bullet.

Roll crimping into a cannelure can hold onto the bullet for an extra fraction of a fraction of a moment and alter the pressure curve.  For taper crimping, it's not going to make a difference.  

 

You could set you crimp die for .378 or .379 and forget about it forever.

 

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Measure the case wall thickness. Say that case wall is .011 inches. Multiply that by 2 (.022), now add that back to your bullet diameter (.355 + .022) and that should be where your "crimp" is..377

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Do a search on BEF, this subject has been covered and answered many times. And often with pictures. 

 

Idescribe has nailed it. 

Edited by HesedTech

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I've never measured the case itself,but I meaure a pulled bullet whenever I adjust the crimp die.  Find the ring in the bullet that was made by the case mouth and measure the diameter. I like that ring to be .003 less than the diameter of an uncrimped bullet. However, as this thread shows, there's plenty of people who don't even like to leave a ring in the bullet at all. Like most things reloading related you will find what works best for you

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Just remove the bell(.378/379) and see if it feeds in all of your pistols.  If it doesn't, take the pistols that it doesn't feed in and go a little more until it does.  I'd consider .376 the tightest I'd personally want to crimp, but a looser crimp has generally delivered better accuracy for me in 9mm.  FMJ's will be less sensitive to crimp than plated/coated options.

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2 hours ago, ajblack said:

 Find the ring in the bullet that was made by the case mouth and measure the diameter. I like that ring to be .003 less than the diameter of an uncrimped bullet. 

 

No one should do this.  This is not how taper-crimping works.  Taper-crimping to a .003 indent is nuts.

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44 minutes ago, IDescribe said:

 

No one should do this.  This is not how taper-crimping works.  Taper-crimping to a .003 indent is nuts.

I guess different strokes paint the world, I've learned that this crimp is what gives me the best accuracy and SD with my bullet and powder combo. I would just reiterate to the OP to find what works best for them with their equipment

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I measure case wall .0105” x 2 plus bullet diameter..355” = .376” finished 

 

Tim

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9 hours ago, ajblack said:

I've never measured the case itself,but I meaure a pulled bullet whenever I adjust the crimp die.  Find the ring in the bullet that was made by the case mouth and measure the diameter. I like that ring to be .003 less than the diameter of an uncrimped bullet. However, as this thread shows, there's plenty of people who don't even like to leave a ring in the bullet at all. Like most things reloading related you will find what works best for you

 

This procedure has proven reliable and repeatable for me with 9, 38SC & 40. I set this to a barely distinguishable .002", but have used .003 with no loss in accuracy.

 

When the taper crimp is pressed in place (tool head & die down on loaded cartridge), this tiny indentation ring is pressed into bullet by the case.

As soon as you lift the tool head & taper crimp die away from the cartridge, the brass relaxes (springs back) a tiny bit... back to the straight wall case you are looking for surrounding the bullet.

 

* I understand the 9 is a tapered wall case, but is undersized during sizing. I measure .350" ID in a sized case where the bullet will be placed, and this is responsible for the tension/hold when the bullet is pressed into place.

 

The best part about this procedure is that it is 100% repeatable. Much easier than trying to accurately caliper the edge of the edge of the case.

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17 hours ago, ajblack said:

I guess different strokes paint the world, I've learned that this crimp is what gives me the best accuracy and SD with my bullet and powder combo. I would just reiterate to the OP to find what works best for them with their equipment

 

It's not just different strokes.

This will cause outright problems with some bullet types.  This can damage coating for coated lead, as well as thin copper plating.  

There is no advantage to crimping past flush, and again, the penalty is bullet damage and reduced accuracy.

 

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39 minutes ago, IDescribe said:

 

This can damage coating for coated lead, as well as thin copper plating. 

I agree, and this is why I find it important to pull a bullet whenever adjusting crimp and verify that the coating is not being scraped.

 

Crimp can adjusted for maximizing efficiency and accuracy just like OAL and powder weight when you're forming your own load data. So what's the problem with a load that shoots clean, has great accuracy, and is reliable if the bullet has a measurable ring in it?  There's all kinds of of coated bullets out there that retain the lube groove and I don't see any issues with those either as far as having a ring is concerned

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46 minutes ago, IDescribe said:

 

It's not just different strokes.

This will cause outright problems with some bullet types.  This can damage coating for coated lead, as well as thin copper plating.  

There is no advantage to crimping past flush, and again, the penalty is bullet damage and reduced accuracy.

 

 

To clarify, while this process does crimp just past flush,

the end result is precisely flush (after brass case springs back).

 

 

 

11 hours ago, racer-x said:

As soon as you lift the tool head & taper crimp die away from the cartridge, the brass relaxes (springs back) a tiny bit... back to the straight wall case you are looking for surrounding the bullet.

 

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6 minutes ago, ajblack said:

I agree, and this is why I find it important to pull a bullet whenever adjusting crimp and verify that the coating is not being scraped.

 

Crimp can adjusted for maximizing efficiency and accuracy just like OAL and powder weight when you're forming your own load data. So what's the problem with a load that shoots clean, has great accuracy, and is reliable if the bullet has a measurable ring in it?  There's all kinds of of coated bullets out there that retain the lube groove and I don't see any issues with those either as far as having a ring is concerned

 

If something works I look for something else that needs fixing :) .

 

FWIW, it seemed like too much crimp had me throwing curve balls. Very good accuracy at 15 yards or so but a greater than expected group size at 30 yards or so.  

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11 minutes ago, IHAVEGAS said:

 

 too much crimp had me throwing curve balls.  good accuracy at 15 yards but not at 30 yards  

 

^^^^   True     ^^^^^

 

Too much "crimp" can adversely affect accuracy, and too little "crimp" can affect feeding    :) 

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First of all it depends on the bullet.  If you are using a plated bullet, they you really only have a soft lead bullet with a thin film around it and too much crimp (which could be normal crimp for an FMJ) can squeeze the bullet so much that you get a bullet that is too small and don't get enough spin by the rifling and this is one good reason to get bullet tumble - I've seen it many time guys who goes from FMJ to plated and do not change their crimp.

 

For a jacket bullet, crimp controls two things (apart from taking off the bell).  One is it can prevent bullet setback in a mag fed gun especially if you use a taper crimp.  Another effect is it affects how much pressure builds up before the bullet is released.  Done in moderation, it allows you to adjust precision.  However, done too much and wrong, you can get into a scatter node. 

 

Also keep in mind that with any crimp, the amount of crimp you get depends not only one what you dial in but the thickness of the brass case.  Case wall thickness can vary by as much as 5 thousands and so using range pickup mix headstamp can get you a big variation in the degree of crimp with the same crimp setting. 

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11 hours ago, IHAVEGAS said:

 

FWIW, it seemed like too much crimp had me throwing curve balls. Very good accuracy at 15 yards or so but a greater than expected group size at 30 yards or so.  

 

Seen it MANY times in here.  Poor bullet to barrel fit and overcrimping cause all sorts of accuracy problems if not outright tumbling.

This isn't 600 meter rifle with jacketed bullets and super slow powders with tall powder columns where pressure builds slowly and let you tune it with an extra thousandth or two of crimp.   It's superfast burning pistol powders in stubby little cases whose pressure curves don't respond to that and where all your extra crimp is doing is denting the bullet surface, and the case of coated lead and plated, damaging the surface.

AND again, as has been said in these forums thousands of times -- extra taper crimp does NOT hold the bullet any better and prevent setback.  Neck tension holds the bullet in place, and like any straight piece of metal, if you bend it inward at the top, it bows out beneath that point in response.  Taper crimping past flush can REDUCE neck tension and INCREASE the likelihood of setback, not decrease it. 

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56 minutes ago, IDescribe said:

 

 extra taper crimp does NOT hold the bullet  and prevent setback.  Neck tension holds the bullet in place

 

^^^^^^   YUP      ^^^^^^^^^^

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