Case crimping too tight?

[racer-x]

Agreed. The sole purpose of the taper crimp is to remove the bell in the case so the cartridge feeds and chambers correctly.

[jlow]

Taper crimp also contributes to neck tension.  ANYTHING that reduce the diameter of the neck and crimps down on the bullet contributes to neck tension.

 

If you taper crimp ONLY to reduce the bell then yes, but if you crimp further then NO.  Please read this article first:

http://bulletin.accurateshooter.com/2015/06/precision-handloading-for-pistols-tips-from-the-usamu/

 

Note where it says:

"Optimize the Taper Crimp
One often-overlooked aspect of handloading highly-accurate pistol ammunition is the amount of crimp and its effect on accuracy. Different amounts of taper crimp are used with various handloads to obtain best accuracy. The amount is based on bullet weight, powder burn rate and charge, plus other factors. It is not unusual for our Shop to vary a load’s crimp in degrees of 0.001″ and re-test for finest accuracy."

Edited January 15, 2019 by jlow

[Hi-Power Jack]

7 minutes ago, jlow said:

Taper crimp also contributes to neck tension.   

 

Interesting article - thanks for sharing.

 

The article's one paragraph on the subject says that crimp affects accuracy, but I don't see any

indication that it affects neck tension.     

[jlow]

It affects accuracy by affecting neck tension, that in turn affects when bullet is released which affects when the bullet leaves the crown of the barrel.  Look up OBT (optimal barrel time) on the web to understand why that is important.

 

We are talking about very slight differences in when the round is released by the case, milliseconds.

[racer-x]

Here is a great link on the subject:

https://czfirearms.us/index.php?topic=78873.0

 

I read up on OBT and it is a very interesting concept for rifles and that last % of accuracy.

12 hours ago, jlow said:

Taper crimp also contributes to neck tension.  ANYTHING that reduce the diameter of the neck and crimps down on the bullet contributes to neck tension.

 

Crimping /reducing the diameter of the neck past the point it contacts the bullet will not increase neck tension as the brass has greater elastic properties than the lead bullet. Brass will spring back (.003), while the bullet will not.

 

Sized brass is (.005 with my LEE dies) smaller ID than bullet diameter. Press bullet into place and it is held with this tension. Brass is stretched .005 to accept the bullet. Area of brass that was belled or flared is a lost cause for 'holding' bullet, and why its best to use minimal bell. Only way to completely remove the flare without deforming bullet is with no bullet in place, but that defeats the purpose of the flare:)

Best you can do with taper crimp is remove flare so the round feeds correctly into chamber... without damaging the bullet and impacting accuracy.

[BallisticianX]

How I setup my crimp for Jacketed bullets. Using new brass that hasnt been work hardened by several firings/sizings (eliminates spring back variable); size a case and do not expand the case mouth. leaving your crimping die backed out and loose in the press bring the sized case into the crimp die (press ram all the way up) and leave it there. Now screw the crimp die down slowly and feel for it to contact the case mouth, back it off just a little and lock it down. now expand the case, seat a bullet and send it through the crimp die. Take the dummy round and measure using Grumpyones mentioned formula of wall thickness multiplied by 2 plus bullet diameter. If you dont have a tube micrometer to measure case wall thickness take a measurement of the loaded round diameter a little more than a 1/16" below the case mouth, note it, and then measure the case mouth, they should be the same and the case mouth profoundly visible so it will properly headspace. Adjust accordingly. As a footnote if you achieve the case mouth measurement target on the first try it could be misleading, disassemble the round with an inertia bullet puller and inspect the bullet for how much of a crush ring is on the bullet. If its substantial back of the crimp die and try again until the mouth measurement grows then you know where your at. Also as others have said bullet setback prevention does not solely rely on the amount of taper crimp, it can add a slight bit of resistance but the case tension is what firmly holds that bullet. As a new reloader know that as cases are fired and re-sized the brass work hardens. As a result you get more spring back and lose some of that case tension. Also straight wall handgun cases tend to shrink with repeated loadings. Oh and different lots/brands of brass vary in length. So monitor your crimp,  if you see less crimp after awhile dont get paranoid the press adjustments changed...probably just cases getting shorter. Hence newer brass for matches, older brass for practice. 

[Bob_072]

On 1/14/2019 at 7:40 PM, IDescribe said:

 

 

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. 

Some good posts on this topic.   I reload 9mm and put the theory to the test.

I took Hornady 115 and 124gr FMJ and crimped them to .  They measured .376 some .3755"

 

I also pulled the bullets from factory Blazer that measured .375.   They had no ring on the crimp.  

 

Now this is far from scientific as I was going for how easy it was to remove the bullets. with a kinetic bullet puller.

The "over crimped bullets with the ring dents where much harder to get out of the brass.  3-4 good raps on the cement to release the bullet.

On the bullets that had no crimp ring only 1 hammer rap was required, they came out so easy I had to do a few more to believe it.

 

So I am not so sure the theory that over crimping makes the bullet looser is correct.  At least in this test it pointed to a stronger hold on the bullet.  

 

I've not conducted a accuracy test but I can see how a bullet with a ring around it might behave differently.  

 

Edited February 23, 2020 by Bob_072

[Hiroshi]

I like my crimp at .378 dia.

[IHAVEGAS]

On 2/23/2020 at 10:28 AM, Bob_072 said:

Some good posts on this topic.   I reload 9mm and put the theory to the test.

I took Hornady 115 and 124gr FMJ and crimped them to .  They measured .376 some .3755"

 

I also pulled the bullets from factory Blazer that measured .375.   They had no ring on the crimp.  

 

Now this is far from scientific as I was going for how easy it was to remove the bullets. with a kinetic bullet puller.

The "over crimped bullets with the ring dents where much harder to get out of the brass.  3-4 good raps on the cement to release the bullet.

On the bullets that had no crimp ring only 1 hammer rap was required, they came out so easy I had to do a few more to believe it.

 

So I am not so sure the theory that over crimping makes the bullet looser is correct.  At least in this test it pointed to a stronger hold on the bullet.  

 

I've not conducted a accuracy test but I can see how a bullet with a ring around it might behave differently.  

 

 

Actual data is good.

 

Another data point, with my 9mm 8 shot wheel gun I shoot 160 grain coated bullets, I always crimp just enough to bring the brass back to the bullet. 

 

Using a Lee undersized sizing/decapping die, bullets do not try to walk out of the brass, using a standard sized die (Dillon in my case) the bullets will walk. In the past I had accuracy issues beyond 15 yards or so that I blamed on overcrimping coated bullets, I was not very scientific about testing but reducing the crimp seemed like it stopped my gun from throwing breaking fast balls with coated bullets. 

 

 

[HesedTech]

Over crimping isn’t just about making the bullet smaller, it’s about damaging the base/bearing surface of he bullet. The bullet’s consistency of the bearing surface has the greatest effect on the accuracy of the projectile. Damage that, change its shape or size will cause problems up to tumbling.

 

In coated or very thin plated bullets an over crimp can also cause the stripping of the surface as the bullet begins it journey down the barrel. If it was just the extra groove dug into the bullets then we would see lube groove bullets have issues and we don’t. 
 

Which brings us back to the Lee FC die in 9mm. It doesn’t over crimp, it literally swages the cartridge down to “factory” specs and does the same to the bullet.  An undersized bullet effects accuracy in a huge way. 
 

All the advice here to only crimp to remove the bell is the way to go (as long as it will plunk).

[K-Texas]

I don't know anyone who trims 9 x 19mm cases. We accept a very slight amount of difference in case-length.

 

Not many segregate cases by brand or thickness, so again, we accept slight variations, but for thickness. Those differences in thickness in comparison to case-length may not be that much different than the variations in case-length.

 

So there's supposed to be a one-size-fits-all solution?

[Cuz]

So with a Lee factory crimp die in my last stage I don’t have to worry about overcranking on the crimp with plated Bullets?


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[HesedTech]

4 hours ago, Cuz said:

So with a Lee factory crimp die in my last stage I don’t have to worry about overcranking on the crimp with plated Bullets?


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Do you mean this die in 9mm?
https://leeprecision.com/reloading-dies/hand-gun-dies/lee-carbide-factory-crimp-die/
 

or is it this one:

https://leeprecision.com/reloading-dies/hand-gun-dies/taper-crimp-die/

 

The first one sizes the entire cartridge including bullets as it lowers to the crimp and the second only does a taper crimp. 
 

The second does a great job with the crimp. 

Edited March 16, 2020 by HesedTech

[shred]

I've never seen a USPSA-meaningful difference in accuracy from crimping jacketed bullets any reasonable amount (even unreasonable amounts as-in the 9x25 Dillon).  30,000 PSI on the back end swages it out unless your lead alloy is hardened-- which it is in many plated and coated bullets.

 

That said, I do get a small steady stream of people complaining my case gauges are too tight and not passing their ammo, yet when I throw a couple sample rounds on the optical comparator, there's an obvious bell and a micrometer shows the mouth is above SAAMI-max size.  If you are concerned about crimp and don't have a comparator or micrometer handy, find a good magnifier and have a look at the crack between the bullet and case.  It should be maybe a tenth of the brass thickness.

 

[Shep]

The crimp subject has caused me a lot of questions when it comes to auto pistols. I am Also fairly new to loading 9mm, and have had mixed results with accuracy, especially with coated bullets.

Does anyone have a preference for the type of crimp/ bullet ? Like a certain crimp that seems to work better for coated and a different for jacketed. At this time I have only used the taper crimp for autos and roll crimp for revolvers, but I did order a lee FCD die yesterday.

[HesedTech]

7 hours ago, Shep said:

The crimp subject has caused me a lot of questions when it comes to auto pistols. I am Also fairly new to loading 9mm, and have had mixed results with accuracy, especially with coated bullets.

Does anyone have a preference for the type of crimp/ bullet ? Like a certain crimp that seems to work better for coated and a different for jacketed. At this time I have only used the taper crimp for autos and roll crimp for revolvers, but I did order a lee FCD die yesterday.

 

Being new to reloading what you need to do is search this forum with your questions first. The whole crimp issue is widely commented on as well as the Lee FCD for different calibers.

 

In a nut shell for 9mm:

1. Minimum crimp, just enough to remove the bell, OD about .378. Doesn't matter what "type" of bullet you are using.

2. Lee FCD for 9mm not used a lot of competitive shooters, especially loading coated and plated bullets. 

3. No roll crimp, just taper.

 

You also need to know not all sizing dies are the same. The "U" dies are popular because they slightly undersize the brass and make it easier to prevent bullet setback.

 

Good luck and enjoy the hobby in these stressful times!

[MemphisMechanic]

@Shep,
If in doubt, set it to .378 with a pair of calipers like @HesedTech suggested. I’ve found that to work well on pretty much everything.

 

The way to verify it as a good setting is to pull a bullet. Particularly with coated or plated it is important to have two things present:

 

1. A very light mark where the case mouth was, or none. You shouldn’t be able to catch your fingernail on it.

2. The bullet should measure the same diameter both above and below the place where the rim was crimped.

 

Also. Keep in mind that 9mm brass varies from roughly .010 to .014 at the case mouth. Some brands will be getting crimped more than others. You’ll notice some variation.

 

Edited March 19, 2020 by MemphisMechanic

[Rallyx100]

5 hours ago, MemphisMechanic said:

@Shep,
If in doubt, set it to .378 with a pair of calipers like @HesedTech suggested. I’ve found that to work well on pretty much everything.

 

The way to verify it as a good setting is to pull a bullet. Particularly with coated or plated it is important to have two things present:

 

1. A very light mark where the case mouth was, or none. You shouldn’t be able to catch your fingernail on it.

2. The bullet should measure the same diameter both above and below the place where the rim was crimped.

 

Also. Keep in mind that 9mm brass varies from roughly .010 to .014 at the case mouth. Some brands will be getting crimped more than others. You’ll notice some variation.

 

I agree, sorting by headstamp makes a difference at case mouth, there will be a variation of neck tension otherwise.

[shred]

16 hours ago, HesedTech said:

 

Being new to reloading what you need to do is search this forum with your questions first. The whole crimp issue is widely commented on as well as the Lee FCD for different calibers.

 

In a nut shell for 9mm:

1. Minimum crimp, just enough to remove the bell, OD about .378. Doesn't matter what "type" of bullet you are using.

2. Lee FCD for 9mm not used a lot of competitive shooters, especially loading coated and plated bullets. 

3. No roll crimp, just taper.

 

You also need to know not all sizing dies are the same. The "U" dies are popular because they slightly undersize the brass and make it easier to prevent bullet setback.

 

Good luck and enjoy the hobby in these stressful times!

 

Agree with most of that-- I've used a Lee FCD for close to a quarter million rounds of competition 9mm and have only one complaint about it--the crimp adjustment on the one I have backs out slightly over time.  Put a mark on it and every time you refill primers,check it hasn't moved or adjust, drive on.

 

 

[AverageJoeShooting]

i didn't even realize putting an actual crimp on an open gun was something people did.  I thought it just straighted the bell out so it could move down the barrel 

Edited March 20, 2020 by AverageJoeShooting

[bodybag0]

On ‎3‎/‎19‎/‎2020 at 4:58 PM, HesedTech said:

 

Being new to reloading what you need to do is search this forum with your questions first. The whole crimp issue is widely commented on as well as the Lee FCD for different calibers.

 

In a nut shell for 9mm:

1. Minimum crimp, just enough to remove the bell, OD about .378. Doesn't matter what "type" of bullet you are using.

2. Lee FCD for 9mm not used a lot of competitive shooters, especially loading coated and plated bullets. 

3. No roll crimp, just taper.

 

You also need to know not all sizing dies are the same. The "U" dies are popular because they slightly undersize the brass and make it easier to prevent bullet setback.

 

Good luck and enjoy the hobby in these stressful times!

I have the Dillon 9mm "U" die.  I hate the bottle shape look of the brass.   I don't use one any more.   But that's just me.