Roll Crimping Cast 45ACP?

[johngalt]

ditto on what has been said about RP brass and crimp.

My biggest source of problems with bullet setback has been with RP brass. It is very thin and doesn't have sufficient neck tension. .452 lead bullets setback less than .451 jacketed but is still a problem. My RP brass has been relegated to my 625.

Increasing crimp doesn't increase neck tension, it decreases it and makes the problem worse. It is best to apply just enough to remove the case flare, so that it feeds reliability.

I am skeptical of the 'heavy rollcrimp' advice for magnum revolver cartridges. I've compared posted pictures with factory loaded .357 cartridges. A lot of the pictures show crimp far heavier than any factory load I've used, and none of the bullets have every jumped the crimp.

Neck tension is important for revolver cartridges too.

BTW, I taper crimp my 625 ammo also, never had a bullet pull out of a case even with RP brass.

 

[rosewood]

We're talking about 45ACP, not 44 Magnum. Two different reasons, and methods for applying that crimp, but I'm sure you already know that. Applying a roll crimp to correct the OP's loose bullet problem is NOT the answer, correcting the improperly sized case is.

Yes, I was responding to the blanket statement that neck tension holds the bullet, not crimp. Now maybe you meant specifically for auto load pistol cartridges, but the statement wasn't clear. As I said, it depends on the gun/cartridge/use.

Rosewood

 

[rosewood]

I am skeptical of the 'heavy rollcrimp' advice for magnum revolver cartridges. I've compared posted pictures with factory loaded .357 cartridges. A lot of the pictures show crimp far heavier than any factory load I've used, and none of the bullets have every jumped the crimp.

Neck tension is important for revolver cartridges too.

BTW, I taper crimp my 625 ammo also, never had a bullet pull out of a case even with RP brass.

I have personally experienced this with a Taurus 450 (ultralight 45 colt). The gun will pull boolits if you do not provide a tight roll crimp even with lighter loads. The gun is just so light. Now maybe the brass is the problem, but the crimp definitely fixed the problem. It did not make it worse.

Rosewood

 

[rosewood]

Not trying to be obstinate, just trying to understand what I am missing here. I have heard the comment before that a crimp reduces tension on the bullet. I do not understand the physics behind that. If you put a crimp on the case which in turn crimps the bullet or goes into the crimp groove, the case has either got to stretch out for the fatter part of that bullet to either go forward or backward or the bullet has to swage down. How does that reduce the force required for the bullet to move? You are creating a physical obstruction to that bullet moving, that creates more friction any way I look at it.

Then this begs the question, why do manufactures put crimp grooves or cannelures on bullets if a crimp has no function? They are in it to make money and surely it cost extra to add that groove that cuts their bottom line.

Rosewood

 

[Nevada Ed]

OP loose bullets.. ;

Old brass wears out and does not spring back like new brass and keep its shape when run through dies. (possible problem)

Too large or too small of a bullets outside diameter can also cause major problems
with the pistol cases when loaded and sized by the dies,
plus how they react to a taper or roll crimp if applied.

In pistol loads, it all boils down to trying to achieve a OAL of the loaded round to fit correctly in the chamber of the pistol being used.

There is the standard, correct way.... #1
#2 may pull a bullet if not fired and then ejected, leaving loose powder to answer to.
#3 in the long run can may cause a broken Extractor tip........
which I am guilty of doing.

I have a Military type 9mm that is back bored so much, that #2 is not a problem, even
if the bullets were loaded longer than what the magazine will accept!!

Each weapon adjust to it's ammo used, per how it was made and it's chamber and barrel spec's.
Crimping can work in some pistols and cause problems in others.
Have fun and stay safe.

 

[johngalt]

Not trying to be obstinate, just trying to understand what I am missing here. I have heard the comment before that a crimp reduces tension on the bullet. I do not understand the physics behind that. If you put a crimp on the case which in turn crimps the bullet or goes into the crimp groove, the case has either got to stretch out for the fatter part of that bullet to either go forward or backward or the bullet has to swage down. How does that reduce the force required for the bullet to move? You are creating a physical obstruction to that bullet moving, that creates more friction any way I look at it.

Then this begs the question, why do manufactures put crimp grooves or cannelures on bullets if a crimp has no function? They are in it to make money and surely it cost extra to add that groove that cuts their bottom line.

Rosewood

Brass is elastic. Bullets are not. If you apply too much crimp, the bullet gets squeezed down. The elastic brass springs back a bit, the bullet does not. The result is reduced neck tension.

Not all bullets have grooves. Lots of jacketed and plated bullets don't. I've seen advice to apply enough crimp to break through the jacket and create a groove. Not the advice I would give.

A roll crimp might help a situation where a bullet is pulling out of a case, but it isn't a substitute for neck tension. I certainly don't think an excessively heavy crimp is needed.

 

[rosewood]

Brass is elastic. Bullets are not. If you apply too much crimp, the bullet gets squeezed down. The elastic brass springs back a bit, the bullet does not. The result is reduced neck tension.

Not all bullets have grooves. Lots of jacketed and plated bullets don't. I've seen advice to apply enough crimp to break through the jacket and create a groove. Not the advice I would give.

Best explanation I have heard. However, unless it springs back completely, you still have a case that is smaller than the bullet before and after the crimp, it is still a physical obstruction for the bullet to move.

Correct, all bullets do not have crimp groves, but many do. There has to be a purpose, much like the reason for a roll crimp for revolver cartridges.

I do not think an overly tight crimp is a good idea either, certainly not breaking through the jacket. That can cause other problems from accuracy to jacket separations. However, I do believe a properly applied crimp in the right place definitely aids in keeping the bullet in place along with neck tension.

Rosewood

 

[Funflyer]

Best explanation I have heard. However, unless it springs back completely, you still have a case that is smaller than the bullet before and after the crimp, it is still a physical obstruction for the bullet to move.

Rosewood

If a taper crimp die is set properly, the only spring-back will be from the belled portion of the case and none below the bell. Now, take that same taper crimp die and try applying a heavier crimp. What will happen is at some point the case will start to bulge below the taper because of the increased downward pressure being exerted on that case. It's this bulge that will have the opposite effect of what you're incorrectly trying to accomplish by adding a heavier crimp.

 

[Funflyer]

In case some of you guys are from Missouri. This is a .452" lead rn in a RP case resized with a Lee U-die. First picture is with just the bell removed with little to no crimp. Second and third pic show a light and heavy crimp respectively. I used a mic w/vernier scale and marked the brass to take the measurement as close to the same spot each time for accuracy. Last pic is the same bullet loaded in a Winchester case to show that the difference in brass thickness isn't very much. So would .0005" make a difference with bullet tension? With the RP brass it easily could and why I don't crimp, only remove the bell. Also, don't count on Lee Precision to make each die to the same tolerance. Some could easily cause more bulge, and some less.