Crimping w/ cast: heavy vs. light

[Boolseye]

Hey Folks,
I know that w/ 9mm a light crimp, just to get the bell out, is preferable. Is this also true with the heavy hitters, say a .44 mag with a gas check? Is there a rule of thumb here? Thanks for your input,
jp

[NSP64]

I was using a very slight resize and a light crimp on my 325 gr 44's and had the #4,5,&6 boolits backing out under recoil. I increased case tension and crimp. Problem solved.

[Hickory]

With fast burning powders like;
231
AA #2
Bullseye
Heavy crimp not really needed for light target loads.

With slower burning powders like;
2400
H 110
296
AA # 9
there is the need for a good heavy crimp to help
the powder to burn better and more completly.

[Bass Ackward]

Crimp performs several functions:

It holds the bullet for recoil.

It centers the front of the bullet in the case if your reloading dies, press, brass or procedures get alignment out of whack.

It aids in ignition.

Ignition is the most controversial step because of case volume and pressure curve which brings bore diameter into the discussion too. Crimp works, diminishing as pressure levels and powder speeds increase up to about 24k psi. Obviously, anneal, brass thickness, length uniformity, bullet design all play a part in the results.

Which is why one guy says phooey on crimp while another swears by it.

[Boolseye]

Thanks for all the input, folks. Can crimp affect leading? It's often suggested with the 9mm to have a light crimp. The reason is leading and bullet fit, ya?

[sqlbullet]

A taper crimp die will size the bullet down further if it is applied too heavily. To check, pull a loaded and crimpled bullet and see if it is smaller with a micrometer. Also, check an uncrimped round, since the sizing can be during seating if the case mouth is not expanded enough.

My general rule of thumb is to just smooth out taper crimp cases, which generally use faster powders. Even my 10mm I rarely get slower than AA#9 or 800X. If I need more pressure to start things up in this case I use a magnum primer and work the load back up , rather than a stronger crimp.

In 357 Mag, 44 mag and 30-06, I apply a rather heavy role crimp.

[mdi]

Crimp performs several functions:

It holds the bullet for recoil.

It centers the front of the bullet in the case if your reloading dies, press, brass or procedures get alignment out of whack.

It aids in ignition.

Ignition is the most controversial step because of case volume and pressure curve which brings bore diameter into the discussion too. Crimp works, diminishing as pressure levels and powder speeds increase up to about 24k psi. Obviously, anneal, brass thickness, length uniformity, bullet design all play a part in the results.

Which is why one guy says phooey on crimp while another swears by it.

Thanks Bass, this is the reasoning I use to determine crimp. I use a heavy roll crimp on my heavy .44 magnum loads and .357 magnum loads. H110/W296 "needs" a heavy crimp for good ignition (even though I've been using WC820 a lot lately I still put a heavy crimp on them).

[mdi]

Thanks for all the input, folks. Can crimp affect leading? It's often suggested with the 9mm to have a light crimp. The reason is leading and bullet fit, ya?

As I understand it, the 9mm headspaces on the mouth of the case and is the reason for a "straightening" crimp, just like the 45 ACP.

[44man]

None of my heavy loads get a "heavy" crimp. I roll the brass into the groove only. Go too far and you cut into the boolit or bulge the brass below the crimp, breaking the case tension.
Case tension does 99% of holding boolits and aiding burn.
Without tension even the most drastic crimp will not hold a boolit.
Too much is attributed to a little roll at the edge of the brass.
There is just no need to go any farther then when the brass is fully in the crimp groove. Even the scratches that Lee calls a crimp groove will hold a boolit if tension is correct. The 400 gr Lee in the .475 will not move.
The crimp will aid tension but will not cure poor tension.

[1Shirt]

Never saw bad advise ever coming from either Bass or 44Man. Lots of experiance and common sense!
1Shirt!

[fredj338]

I doubt you can taper crimp enough to resize a bullet, there is only a slight reduction at the case mouth. As noted, roll crimping passed a certain point actually does bad things like loss of neck tension & case bulging. There is a lot of controvercy on the LFCD resizing the bullet along w/ the case, but, at lest in 45acp, doesn't seem to affect medium-medium hard cast lead bullets. Pull a seated & crimped bullet in the 9mm, if you can see a clear emdedded line, it's too much crimp.

[btroj]

I am with 44man. Case tension is the key, not the crimp. I think of the crimp as the finishing touch but it alone won't give the bullet pull needed in some applications.
If pull is not enough then try to polish the expanded to decrease the diameter.
I like enough tension that you can see the grooves in the bullet in the loaded round. This is critical in rounds like the 44mag as it gives the pull needed for a proper burn with the slow burning powders this cartridge likes.

[bhn22]

I match the crimp to the powder manufacturers recommendations. 296/H110 for example requires a heavy crimp, and I make sure the get 'em. A taper crimp isn't even really a crimp, all it does is remove the flare from the case mouth and push the case mouth slightly into the bullet to help prevent the bullet from getting pushed back in the case during a semi-autos feeding cycle.