What is the correct amount of crimp in thousands of inch?

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costantino

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Hello there,
What would you recommend as the correct amount of crimp for auto pistols (glock and 1911 norinco clone) to ensure proper feeding and correct pressures? Do calibers such 45 acp and 9x21mm differ in terms of recommended crimping?
I got myself a neat Vernier Micrometer on E-bay for this task. It it correct to measure the difference between the crimped mouth and the diameter of the case shoulder almost at the bottom? So far I believe on my 9mm I have a difference of 0,008 inch. Does it sound reasonable?
Thanks very much for any help.
Regards,

Costantino
 
I must confess that with my eyesight it is not always obvious to distinguish the absence of any belly on the case :) . Could I rely on the instrument's reading instead?. Thanks again.
Regards
P.s.

I use TC dies on both 9 and 45 but I run this last one thru a factory crimp also.
 
The amount of crimp that I put on my .45 ACP and 9mm X 19... The .45 ACP measures .471 - .472 at the mouth of the case on a finished round. The 9mm X 19 measure .378 - .379 at the mouth of the case of a finished round. Does this help?:)
 
yes yes

Exactly :) ! I wanted to be sure not to have thrown away 5 english pounds on a nice imperial second hand micrometer...
Thanks so much, regards.

Costantino
 
"english pounds"?? Aah...Thought check here. My measurements are in "American inches" as in "point four hundred and seventy-one thousands of an inch" (US SAE).
 
Case wall thickness X2, plus the bullet diameter. No more, no less. Autoloading pistols don't get 'crimped', they have the bell removed from the case.
 
If autoloading ammunition doesn't get crimped, why does Lee supply the factory crimp die with thier deluxe pistol sets. I ask because I just got some 9MM dies and haven't used them yet, but will in a couple of days. I need some advise also.
 
Funny- I just rec'd some Horndy Taper crimp dies and was measuring my commercial CCI .45 ACP and the home made ones. They all were .471" +/- a tad at the mouth.
 
Ok, I am sure I don't want to over crimp the cartridge but the drawing I am attaching comes from the Dillon 650 manual. Proper crimping is achieved in the bullet in the middle (#2) . To me it doesn't look like only the belling has been removed rather than I modest amount of crimping has instead been applied...
By the way, my RCBS dies are TC ones, is the Lee Factory Crimp a taper or a Roll crimp? Could this die be used just to resize the finished ammo without applying any fiurther crimp(ie. without turning clockwise the knob) ?
Nice thread anyway :) !

figure_070b.gif
 
O K...No one ever said dillon was perfect.:rolleyes: Least of all me. Just make sure you have an edge of the case mouth exposed just in case your .45 ACP and 9mm headspace on the case mouth.:scrutiny:
 
There are two primary differences between a factory crimp die and a standard crimp die. First, the factory crimp die does not have a seating stem. Second is the factory crimp die has a carbide ring in the bottom that sizes the case as it passes over it. It is intended to ensure that the case isn't out of shape enough to cause a problem. If the preceeding operations are done correctly the factory crimp die won't touch anything until the crimp ring contacts the case. If the preceeding operations aren't done correctly the factory crimp die will size the case.

You most certainly can overcrimp with a factory crimp die. If you follow the instructions to the letter the odds of this are pretty high. In my experience the directions have you crimping the case mouth into the bullet a couple thousandths, a visible crimp is the result and that is WAY too much for an autoloading pistol cartridge. If you try to set it up like any other die it is pretty easy to overcrimp too. Set the body like the directions say, and then set the crimp to JUST lay the case flat against the bullet.

I don't recommend the use of the factory crimp die, it isn't needed. A standard crimp die is all that is needed.
 
Well Bullet...What can I say. I was just involved in a discussion on whether the .45 ACP/9mm X 19 headspaces on the extracter or the case mouth. I'm a case mouth man myself.:what:

I'm glad I entertained you...:D

And I agree with HSMITH about the need of a FCD for auto ammuition. It's just not needed if you already have a seating die that crimps too. Just enough crimp to remove the bell. No more, no less.
 
Crimp and Headspace on Auto Cartridges

Bushmaster is absolutely right. they headspace on the casemouth.(Straightwalled cases)
I put enough crimp on them so that under a magnifying glass I can see a slight taper crimp.
As HSMITH says-- if it is readily visable to the naked eye it is too much crimp.
 
Last edited:
Measuring the OD (outside diameter) of a crimped case

is not a valid measurement for determining extent of crimp. Bullet diameters vary from bullet to bullet, style to style, and manufacturer to you get the picture. Ditto cases. Wall thicknesses vary. The Speer Manual says that a slight taper crimp can be used but a slight roll crimp can also be used in most guns. In some guns the .45 ACP headspaces on the case mouth, and in others it does so on the extractor. A taper crimp is going to be best on those headspacing on the case mouth for the simple reason the headspace edge in the chamber needs a case edge to mate with. A roll crimp may allow the case to seat too deeply in the chamber. If the case headspaces on the extractor the crimp is irrelevant (to headspacing). A crimp needs to be just tight enough to remove any "belling," hold the bullet in during handling and prevent setback during recoil. Trial and error is the case. You can test the crimp by pushing the bullet gently onto a hard surface such as the side of your bench. It shouldn't move into the case. Practice with this using empty (no powder), unprimed cases until you get the crimp right.
 
Moxie...I have found that if you are within .468 and .474 on .45 ACP that you will have no problem chambering in any Forty-five auto.

And there is no .45 ACP auto pistol that headspaces on the extracter. Those .45 ACP auto pistols based on Colt .45 ACP (1911) use the extracter to insure that round will not fall out if the gun is fired upside down. The round engages the extracter as it is stripped from the magazine. A military requirement of long ago when the Colt 1911 was sold to the military. It gives the impression that it headspaces on the extracter, but does not. Think about it. I know of no extracter that could withstand the sudden slamming of the fired round for very long. Not to mention not enough surface area and the possibility of partial primer back out...
 
"Bullet diameters vary from bullet to bullet, style to style, and manufacturer to you get the picture. "

Not by more than a thousandth or so.
.451 is the only thing I have ever seen on a jacketed .45 caliber bullet.
You can get .452 cast and poorly cast bullets might be all oover the place but they are defective.

Bullet diameter (you can measure it if you are worried it varies) + twice the brass thickness at the mouth.
 
moxie
A crimp needs to be just tight enough to remove any "belling," hold the bullet in during handling and prevent setback during recoil.
Click to expand...

I believe that the case tension is what prevents bullet setback not the taper crimp.
 
The fact that a round chambers well does not mean that it

necessarily has a good crimp, although, you're right, for practical purposes it usually does. Yes, we're talking thousands of an inch here. No, case tension will not always prevent bullet setback without a "good" crimp.
 
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