general concepts behind different crimps?

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general concepts behind different crimps?

Post by Aprilian on 5/5/2017, 3:39 pm

I am trying to understand taper crimps and recently read a thread which included Jon mentioning that lead and jacketed rounds are crimped to different measurements. here

As I come up to speed on crimp concepts, I feel that I understand ;
* how to measure
* how different length brass impacts crimp
* why excess crimp can damage bullet and - if taken far too far - the case
* how thicker brass increases impact of crimp on the bullet

But I can't seem to wrap my mind around why using the same 0.4695 crimp for lead and jacketed is not a good idea.   What is the underlying reason for less crimp on jacketed, it seems contrary to the .451 vs .452 diameter?

I also saw a thread, perhaps on another site, that excess muzzle flash and sooty fired brass were indications of insufficient crimp.   Is there any validity to that idea (it seems like there are many other variables which could drive that end-result)?
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Re: general concepts behind different crimps?

Post by LenV on 5/5/2017, 6:04 pm

Well there wouldn't be much difference if your going with that little of crimp. I crimp the lead bullets down to .463. You wouldn't want to try crimping your jacketed down that far. And you wouldn't need too.
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Re: general concepts behind different crimps?

Post by SteveT on 5/5/2017, 7:35 pm

Soft lead bullets should not generally get much crimp (or any) as it will deform the bullet.

Most "modern" target loads (meaning in the last 10-20 years) recommend light or no crimp.

In general a tighter crimp will hold the bullet stationary longer and (probably) slow the bullet movement so the chamber pressure builds up higher. This will result in more complete powder burn so there will be less ash, un-burnt powder, soot and possibly muzzle flash.

I suspect that a light crimp releases the bullet more consistently. If the brass has the deform to release the bullet that would probably not be as consistent. This is my best guess as to why most target loads use little or no crimp. If the bullet has to deform to get past the crimp (as with soft lead) it would be even more inconsistent.

I don't try to measure crimp with calipers anymore I have 5 marks on my die to indicate no crimp (#1) to heavy crimp (#5). I did it by taking the longest case out of a few dozen that had been sized and deprimed, flared the case then progressively lowered the crimp die until I could put a straightedge along the case and there was no longer any flaring (I used a magnifier). I marked the die position, then cranked it down until it was a significant crimp (probably around .465" or so) and marked that point. There is about 100-120 degrees rotation between the 2 positions. I then made 3 more marks evenly spaced between them so I have 5 marks indicating none to heavy crimp. Then I set the die to the light mark (#2) and haven't touched it since.
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Re: general concepts behind different crimps?

Post by Magload on 5/5/2017, 8:12 pm

Just read a article in the new Blue Press on crimping plated bullets and to me it would seam like a good idea for soft lead.  The object being not to crimp to tight and deform the plating.  The instructions say to start with no crimp and add crimp till they will just drop into a gauge and fall out when it was turned over.  I ran out of Zero 148gr HBWCs but have a thousand X Treme plated DEWCs and they should be just fine for practice on the SL and VSL (very short line 15yds).  I just coined VSL because that is where we shoot the TF & RF from in the monthly club shoot.  I think at 15yds rocks would work if they were nearly the right size.  BTW when they dropped in and fell out fine I added a little more crimp and pulled the bullet to check it.  Now to see how these shoot at the LL next week.  Don
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Re: general concepts behind different crimps?

Post by james r chapman on 5/6/2017, 7:30 am

Another old technique is to crimp to a point where bullet movement is prevented when pressed against a hard object like a loading bench.
Also, leave a cartridge unfired in a magazine to test for bullet movement.
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Re: general concepts behind different crimps?

Post by LenV on 5/6/2017, 9:35 am

Steve T wrote  "Soft lead bullets should not generally get much crimp (or any) as it will deform the bullet "

Sorry Steve I disagree. This is an opinion only but what I have found is that it is more important to get a good solid crimp on a soft lead bullet. I have heard the argument about deforming the bullet but I guarantee that the deformation is less then the lube groove right behind the crimp. I agree that you need a uniform crimp but a light crimp does not guarantee a uniform crimp. Unless you sort cases by length it is very possible to get between none and a bunch of crimp. The longer crimp guarantees a more uniform crimp. Like I said this is just my opinion. The picture below shows my crimp on a 200gr LSWC.

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Re: general concepts behind different crimps?

Post by 243winxb on 5/6/2017, 9:42 am

Crimp doesn't do much to keep the bullet from moving in a 45 acp. IMO.  

The neck tension does. 

Different brass will produce from loose to 45 to over 100 pounds needed to move a lead bullet. 

If there is a crimp groove on jacketed, the crimp would be a little more than lead with no crimp groove.

But taper crimp is not a roll, so just remove the bell enough so the rounds feed without problems.   

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Re: general concepts behind different crimps?

Post by 243winxb on 5/6/2017, 9:59 am

The 45 acp is said to head space on the case mouth. Over crimping may not be good. 

  Some say head space is  on the extractor, not case mouth. Depends on what side of the fence your on. Whats on target , is what counts. 

A custom barrel, with minimum chamber  head space may just let the case head space on the case mouth??
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Re: general concepts behind different crimps?

Post by LenV on 5/6/2017, 10:42 am

Just did a quick search. We have had 13 discussions on this forum about the "crimp". I suspect we will have more.

LenV
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Re: general concepts behind different crimps?

Post by Magload on 5/6/2017, 10:56 am

LenV wrote:Just did a quick search. We have had 13 discussions on this forum about the "crimp". I suspect we will have more.

LenV

I was adding to this one.  I sit here and typed for 15 minutes and hit send.  Showed that it went so I went back to the home page and it didn't show up.  But another post did.  i have had this happen a lot and think if two post are made to the same thread at the same time mine doesn't show up.  So you all are just going to miss out on my worde of wisdom covering plated and coated bullet crimps being like soft lead bullets.  My trigger finger is just to tired from all this typing as I know that I do get a little verbose on my post.  Don
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Re: general concepts behind different crimps?

Post by Aprilian on 5/9/2017, 4:28 pm

I had some learning time in the loading cave this afternoon.   

I had loaded some JHP for a six-way test of COAL, crimp and powder weight.   I had checked all rounds in a Lyman gauge as I built them.  The rounds with less crimp dropped in the tester cleanly and dropped out, even after a quick push to make sure they were fully inserted.   Strangely, the rounds with more crimp hung up in the gauge and sat slightly lower at the hood, indicating the case mouth was slightly sliding past the end of the gauge "chamber".   

Something seemed strange so I took the barrel out of my pistol and checked with the barrel and got the exact opposite result!   The rounds with less crimp dragged in the chamber, then stuck and the round with more crimp dropped in and out clean.   

I took some of the larger rounds and slowly added crimp until they dropped cleanly in, couldn't be pushed farther in and dropped out cleanly.   It looks like my barrel like a minimum 0.468" crimp (measured with the jaws barely going over the edge of the case mouth).  I can see the cases are less than perfectly straight (tapered in slightly at the mouth).   
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I now don't plan to use the Lyman tester as 0.468" slips in too far and hangs up.


Last edited by Aprilian on 5/9/2017, 6:27 pm; edited 3 times in total (Reason for editing : grammar again)
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