RCBS Die Question


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CustomGunworks
January 2, 2008, 04:46 PM
Can anyone tell me the difference between a roll crimp and tamper crimp
on a cowboy die set in .357/38 ?

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Urbana John
January 2, 2008, 05:17 PM
This is my thought----a taper crimp is kinda like an upside down funnel, meaning the more you turn the die down or the farther up into the die, the "firmer" the crimp.

The roll crimp has a "step" inside the die and the seating and the OAL of the cartridge, must be set together.

I load a 200 gr. 45acp bullet for my 45LC and have to use a taper crimp,since there is no knurl on the bullet.
The bullets I use for my 357 have a knurl, and if the OAL of the case is correct, and if you use the roll crimp into the bullet's knurl, your OAL cartridge is usually correct.

UJ

loadedround
January 2, 2008, 07:54 PM
I would like to shed a little more light on this subject if I may. The roll crimp was designed to be used with a revolver bullet or any other bullet the has a crimp grove or "cannalure". As said previously the case is slightly folded into the cannalure to hold it in place. The taper crimp is used on all semi auto cases that head space on the case mouth, the two "biggies" being the 9MM NATO and the 45 ACP; the taper crimp just tensions the case mouth around the case mouth and does not fold the mouth in. If it did the the loaded round would be forced deeper into the chamber and you would hava FTF. The taper crimp die can also be used with any bullet with or w/o a cannalure. Most OTC die sets are sold with the taper crimp die or seating/crimp die, supposedly because it is easier to set the "perfect" crimp.
If one is loading for a revolver and using cannalured bullets, specify the type of crimping die wanted. Some 30 years ago, almost all dies were of the roll crimp variety. :)

Sunray
January 2, 2008, 08:28 PM
"...have to use a taper crimp, since there is no knurl on the bullet..." A taper crimp(and only a taper crimp) is used on an ACP(or any rimless cartridge used in a semi-auto pistol) because it headspaces on the case mouth. The bullet has nothing to do with it.
A roll crimp bends the case mouth into the bullet by rolling the case mouth. It's literally rounded.
A taper crimp is just that. A taper. The case mouth is pushed into the bullet with no rolling on a slight angle.

Urbana John
January 2, 2008, 08:37 PM
Sunray----You are right about "any rimless cartridge used in semi-auto pistols/rifles" because it headspaces on the case mouth, but how can you "push the case mouth into the bullet???????
I have better luck, when reloading, trying to push the bullet into the case mouth!!
UJ

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