Do I have the "crimp" thing right?

[Col Defender]

Hi - For most calibers I roll crimp my revolver cartridges with RCBS dies (seat and crimp in one operation) and follow their instructions on die adjustment precisely.

?
But their instructions are not clear on how much roll crimp is enough. I have gotten into the habit of putting more crimp on a powerful cartridge like .44 Mag, less on .357, even less on .38 Spec and least of all on .38 S&W.

Is this OK? How much is enough anyway??? I know too much crimp can crush a case but what happens if there is not enough crimp. And how to know?

FWIW I recently got a Lee Factory Crimp die for 38/357 and already have one for .45 ACP but all the other calibers I still do in one operation with a single seating/crimping die.

Thanks

Steve

 

[Scrapper]

I would say with the roll or taper crimp you cant really over do it cause of the limitation of the die. You can only crimp so much before you either crush the case or the bullet. Some where in between is probably good.

I have good eyesight and still have a magnifying glass handy when checking things like this(easier on the eyes).

Here is a thread on some crimping not exactly about this but any crimping info is always good to read.

http://smith-wessonforum.com/reloading/112798-lee-factory-crimp-cast-bullet-modification.html

 

[BruceM]

For revolver cartridges, you have enough crimp when the bullets will not move in the case during firing. Load a cylinder full of your reloads, shoot four and check the remaining rounds for bullet movement. If they did not move, you have enough crimp.

Incidentally, do not confuse tight bullet pull with crimp. Bullet pull is neck tension between the bullet and case neck. Tight bullet pull is necessary for complete combustion of slow burning propellants. Crimp is used to prevent bullet movement during the firing cycle. These are two different things and the terms should not be used interchangeably-same concept as clip vs magazine.



Bruce

 

[Skip Sackett]

This should be a sticky!

For revolver cartridges, you have enough crimp when the bullets will not move in the case during firing. Load a cylinder full of your reloads, shoot four and check the remaining rounds for bullet movement. If they did not move, you have enough crimp.

Incidentally, do not confuse tight bullet pull with crimp. Bullet pull is neck tension between the bullet and case neck. Tight bullet pull is necessary for complete combustion of slow burning propellants. Crimp is used to prevent bullet movement during the firing cycle. These are two different things and the terms should not be used interchangeably-same concept as clip vs magazine.



Bruce

This is sage wisdom friends. Make a note of where to find this!

 

[Cary]

+1 on the statement Bruce made. There is a following out there that believe the harder you crimp a case the more bullet pull is increased.
Cary

 

[flat top]

...........and I am one of them. In our and others tests over the years, we have found that compression yield and pull strengths are both increased by crimp pressure.

 

[oldRoger]

I agree with flat top, size+crimp.
Interesting, I have an old copy of Lymans first cast bullet handbook.
I am loading some .357 cases with 148 gr HBSC and was doing a little research. This "golden oldie" recommends full length resize, minimum neck expansion, and a firm crimp, especially for target rounds. Further, a couple of the oldies recommend separate crimp.
Now I am aware that these recommendations are the current received wisdom, my surprise is that it's ancient history as well.

 

[Skip Sackett]

It takes more than crimp!

The point that Bruce, Cary and I are trying to make is that the crimp is not a fix all.

Too many folks try to overcome other inadequacies in their reloading practices by applying a heavier crimp. The crimp, even this new fangled super uber crimp isn't a cure for too little case/bullet friction. If the case is too big or the bullet too small, you can apply all the crimp you want and you are just trying to put make a silk purse out of a sow's ear.

It just ain't gonna happen.

 

[sonny]

Good advice up there in previous posts:

Proper roll crimp

Overzealous crimp IMHO:

A terribly-important part is the initial resizing of your brass, which must size the brass i.d. to at least 0.004" less than the o.d. of your cast bullet. You gotta make sure that your powder expander die doesn't open it back up when you put in the powder. The crimp comes later and works as an insurance policy to hold onto that bullet, so it doesn't begin to slip out of the case mouth, from recoil of other shots, before you fire that cartridge.
You can also see, in the first pix, the profile of the base of the bullet in the case. The portion of the case holding the bullet is slightly larger in o.d. than the case which doesn't hold the bullet. This indicates that the resized case i.d. was smaller in size than the bullet which was loaded into it.
It is also helpful to know that some commercially-cast bullets have a much deeper crimp groove than other bullets. It helps to buy the ones that are deeper. And too harsh a crimp, as seen in the second pix, tends to squash the crimp, to square it off, and to begin to lift the case mouth away from the bullet. Not good, IMHO. This is no longer a roll crimp.
Sonny

 

[oldRoger]

Some where in the distant past, some gunwritter was trying to sell the idea of not resizing 38 spl brass, this would have been in reference to target shooting, probably with what I consider to be the standard 2.7 grs Bullseye behind 148 gr HBWC. In this case too, you would probably be using the same five chambers in the same K38. The scheme as I remember it was de-cap, prime, load powder, shove bullet in, instant success was claimed.
It is very unlikely that this scheme worked for anyone. I tried a few, mostly they will chamber, in some cases there is a bit of neck tension. The time you might save and the theoretical reduction in wear and tear on your brass in no way will compensate for the loss in accuracy.

On the other hand you can be quite successful with full length resize and a slight crimp.
But I am not sure of any case with straight case brass where you are better off with a minimum crimp.

 

[flat top]

Old Roger is correct. Ancient history that still applies today.........and, I dont think anybody here mentioned the crimp being a "fix all". It is just another part of the process that requires attention to detail........ I will take that "new fangled super uber crimp" anyday for the heavy for caliber bullet, top end loads that I shoot...it works for me!!!