confused on crimping

[Dueling1911s]

hi everyone, i'm new to the forum

i just started reloading last week and am all confused on crimping. I'm loading 40 and in the near future 10mm. I'm using a rock chucker and rcbs carbide 40/10mm dies. I'm using a variety of once shot federal, winchester, and monarch brass casings. using ranier 180gr fmjs

I have the speer #14 book and the lyman #3 handgun book
the speer book goes into too much technical info that goes out the other ear. the lyman book is too vague.

any advice would be appreciated

 

[rcmodel]

Look at either manual at the SAAMI cartridge drawing for either caliber.

It will show a .423" MAX case mouth dimension.

You want your taper crimp die adjusted down just .002" to .003" less then that.
Lets call it .420"+.421" shall we?

The taper crimp die should just straighten out the case mouth bell, without compressing the case into the bullet jacket.

rc

 

[rsrocket1]

You really don't need to crimp 40 S&W or 10mm if you are shooting them in an autoloader. If you size the cases properly, you should have enough case tension to hold the bullets in while the pistol is recoiling.

You typically crmip revolver rounds to prevent the bullet from jumping out while they are in the cylinder and jamming it. In a lever action rifle, you crimp in order to keep the stacked bullets in the tube magazine from collapsing into itself.

The only operation you may need after seating the bullet is to use the crimp function of your seating die or a separate factory crimp die to remove any flaring of the case you put in prior to seating the bullet. For that you just screw the die in just a fraction of a turn beyond contact with the case.

 

[1SOW]

Duelling1911,
rcmodel+1

To run a simple test: take a "sized case" (no powder & no primer) and seat a bullet. Measure the case mouth. This is the size the crimp should give with that brand of case. Other brands may be a little thicker or thinner, but that's not significant.

This test case had NO FLARE, just full contact with the bullet. That's what you want "after" the belling is removed by the crimp die. Adding a .001 or .0015 is fine, no damage done. When using plated rounds the crimp size is more important so the plating is not damaged.

 

[steve4102]

The "crimp" on a 40/10mm is only enough to remove the flare applied with the expander die, plus maybe .001-.002 more. It is not used to secure the bullet. "Crimp" is actually the wrong word for this process, it should be called "flare removal" as you do not force the case mouth into the bullet or bullet cannelure.

 

[ColtPythonElite]

What they said...Just remove the bell. As a test, take the barrel outta your gun and make sure you round drops freely into the chamber.

 

[Dueling1911s]

ok, i've been watching crimping videos on you tube. and have a few more questions

why would someone use a separate crimp die when the seater die can crimp?

and why would a semi auto pistol cartage die have a roll crimp in it instead of a taper crimp?

what type of crimp is in a rcbs carbide 40/10mm die?

 

[rcmodel]

A standard auto pistol die will be a taper crimp. That is what the RCBS 40/100mm should have, unless you order the wrong dies and get one with a roll crimp seater.

You might want a roll crimp die if you were shooting a revolver chambered in one of the auto pistol calibers, such as a .45 ACP/.45 Auto rim in a S&W 625. The roll crimp holds the bullet in place against heavy recoil pulling them in a revolver.

A separate seater die and crimp die might be used with cast lead bullets.
That way, the crimp portion of the die isn't trying to close up the case mouth bell before the soft lead bullet is where it is going to be when it crimps.

The result can be shaving lead off the side of the soft bullet with the case mouth.
Not necessary with jacketed bullets.

BTW: The only thing that is "carbide" in a carbide die set is the sizing die interior.
The other dies are just the same as you would get in a non-carbide die set.

rc

 

[GLOOB]

The taper crimp die should just straighten out the case mouth bell, without compressing the case into the bullet jacket.

Technically, in order to completely remove the flare, the die HAS to compress the case into the bullet plating a bit, because of the inherent elasticity/rebound of brass. If you pull a taper crimped round, you will more than likely see a compression ring in the plating.

You really don't need to crimp 40 S&W or 10mm if you are shooting them in an autoloader.

This is completely dependent on the specific firearm in question. The chamber could be cut so loose it doesn't matter. Or the chamber could be so tight that an uncrimped round will not chamber, freely.

A separate seater die and crimp die might be used with cast lead bullets.
That way, the crimp portion of the die isn't trying to close up the case mouth bell before the soft lead bullet is where it is going to be when it crimps.

Even jacketed and plated bullets can deform when seating/crimping at the same time, particularly if the seater plug doesn't fit well. Jacketed hollowpoints and plated FP's are especially susceptible, when seating with a round seater plug. Aside from closing up your hollowpoints and making your FP's look funny, it can lead to large variations in your OAL.

 

[PO2Hammer]

I load the .40 and 10mm with the RCBS dies. The RCBS seater/crimper die has a taper crimp.

I have added the Redding Competition seater die and a Redding taper crimp die. The Comp. seater is not needed, but I get fewer scrapes on plated bullets and it makes changing from .40 to 10mm or different bullet styles a breeze. I removed the seating stem from the RCBS seater/crimper die and use it to crimp my .40 loads. I use the Redding taper crimp die to crimp my 10mm loads, that way I don't have to adjust the dies back and forth when I switch from 10mm to .40.

When using jacketed and plated bullets I set mine up so that the flaring cone on the expander stem just touches the case mouths, opening them up just .003" or so and removing any dents. I have to hold the bullet in place as it enters the seating die, but the minimal flaring/expanding ensures good bullet tension (case grip on the bullet). This helps prevent bullet set back (bullets being pushed deeper into the case when the cartridge hits the feed ramp in the gun)

I set up the crimpers to just touch the mouths and make sure any trace of flare is removed and any dings are pressed in.

I test for bullet set back by making up dummy rounds, no primer-no powder, and cycle them into my gun from the magazine by pulling back hard on the slide and letting it fly forward, like it does when the gun cycles during live firing. Measure the rounds before and after, and make sure they don't set back by more than .005" or so.

 

[1SOW]

One last point, If you're using range brass, the used cases vary in length, so the taper crimp will also vary as longer cases will seat deeper in the die. There will be some differences in your taper crimps.

What juuuust takes out the bell on a short case will add more crimp to a longer case.