Understanding Crimping with Seating Die

S

sirgilligan

New member
I have to know how things work. Being new to reloading I spent some time recently trying to get a proper crimp on my .223 rounds. I know, many say it isn't needed, but I wanted to learn how to do it. Yes I buckled a couple of shoulders. I couldn't figure out why that happens. I tried to imagine what was happening inside the die and I was baffled.

Well, I found two cut-away pictures of a die and now it is very obvious what is happening.

{See board policy on posting copyrighted material.}

I thought others might want to see.

That explains everything to me!

Well, I drew my best interpretation of the copyrighted image, which was a cut-away of an actual seating die.

seating_die.png
 
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Like they say, "A picture is worth a thousand words."

You might want to change the wording on your thread title to "seating die" instead of "sizing die". jd
 
Pictures show seating dies. Sizer dies don't have a place for a bullet to be.
Seaters can push the shoulders down if the die is down too far. And you aren't the only one who has done it. Still have a few .30-06 with, um, broad shoulders, I've yet to decided what I'm going to do with. Keep 'em as an object lesson. snicker.
 
SEATING Die not Sizing Die

Fixed mistake in title.

Yes, that picture is worth 1000 words. It is now easy to see why turning the seating die in too much causes the shoulder to buckle, it has no place else to go.
 
Yes, that picture is worth 1000 words. It is now easy to see why turning the seating die in too much causes the shoulder to buckle, it has no place else to go.
Click to expand...

And-- the same pic could be used to demonstrate the problem that might occur when an over-length case is chambered and fired in a rifle. jd
 
The picture is worth 1000 words, but also, possibly, a few dollars to the copyright holder. You need have to have permission from the copyright holder and also to name the source (an attribution) to put copyrighted materials up on the board. See the board rules on posting copyrighted materials. I know it's an inconvenience, as I used to use images that way all the time, but lawyers have seen to it this is no longer without risk to the board owners for allowing it.

You may be able to make an illustration of your own, though.
 
I will see if I can get an image that is known to not be a copyright violation.
Sorry about that. I was just very excited to see how it worked.
 
My rule of thumb for standard seating dies set to not crimp case mouths into bullets is:

1. Put an empty sized case in the shell holder.

2. Raise the ram to its top.

3. Screw the seater die into the press until it just touches the shell holder.

4. Back the die up 1/4 turn (so its crimping shoulder's about .018" clear of the case mouth and won't even come close to touching it).

5. Lock the die in place.

6. Adjust the die's seating stem to seat bullets to desired cartridge overall length.
 
My drawing of the cut-away image

seating_die.png


It is that small taper in the seating die right at the rim of the case mouth that bends the case into the cannelure.

It is clear to me how I have messed up the shoulders seeing this. Imagine as you turn the die in further (deeper) how that taper forces the case neck straight down, and one of the places that will give way is at the shoulder.
 
It is clear to me how I have messed up the shoulders seeing this. Imagine as you turn the die in further (deeper) how that taper forces the case neck straight down, and one of the places that will give way is at the shoulder.
Click to expand...

this also highlights the importance of trimming bottleneck brass to a uniform length. the same thing can happen with brass that is taller than the rest if you don't have the crimp ring raised high enough
 
I generally don't use my seating die to crimp my cases. I prefer to use the Lee factory Crimp die that was included in my sets. it's an extra step but I like the end result.
 
This depends on a number of things going EXACTLY CORRECTLY...

The big one is,
ALL THE CASES TRIMMED TO EXACTLY THE SAME LENGTH.

Too short of a case an no crimp.
Too long of a case and you get a buckled shoulder.

In a progressive press,
And even in a single press,
The answer is often a 'Factory Crimp' die like Lee makes.

Since I DO NOT trim the brass for length every time,
Instead, shooting them a couple of times,
Then trimming to MINIMUM,
Then NEVER having to trim again, saves a TON of time!

The factory crimp type die DOES NOT care what the lenght of the brass is.
It's a 'Collet' type crimper that pushes from the OUTSIDE of the brass,
NOT DOWN ON THE BRASS,
So you NEVER have a buckled shoulder.

In progressive presses, it's MAGIC for turning out rounds at speed WITHOUT CUTTING BRASS, AND WITHOUT CASE GAUGE TESTING EACH AND EVERY ROUND CRANKED OUT TO SEE IF IT WILL CHAMBER OR NOT...

This makes it VERY handy for cranking out my practice and varmint rounds in VOLUME without failures.
 
I am 15 or 16 years into reloading and own 300 dies tracked in a spreadsheet, only a few are home made, none of the seaters are home made.
I still think that it is possible to seat a bullet and crimp in the same operation, just not by me.
I still need two steps:

1) I seat the bullets with the die high in the press and seating stem low in the die. That seats the bullets to the right depth and keeps the crimp part of the the die not engaged.

2) Then with the same die readjusted or a similar seating die in another press... I crimp the round with the die adjusted just low enough in the press to roll crimp it right with the press handle all the way down. The seating stem is adjusted high in the die [or removed] so the stem does not touch the bullet in this step.

*The two step process above is how it is for revolver ammo that wants a roll crimp.
*I do not crimp most rifle ammo, but 44 mag and 45 Colt rifles like a roll crimp.
* Semi auto pistol ammo gets either no crimp or a lee handgun factory crimp.
*There are some extreme exceptions, like when I Lee rifle factory crimp revolver ammo upside down in the die with dummy rifle brass below. Or where i have a second press upside down and pushing a ram that forms the bullet from round ball to flat nose cylinder as it seats.
 
The rifle probably doesn't need the crimp,
But I get better consistancy in velocity with a medium heavy crimp.

Don't ask me why, it just seems to be that way.
The high/low velocity spread closes up,
While average velocity stays about the same.

Just a quirk? I don't know.
Don't know what others have seen, but this is my experience.
 
It is so easy to seat and crimp at the same time especially if your bullet has a cannalure.

I can usualld set my die up with one cartridge. I drop the powder set the cartridge in the shell holder and then turn the die into my press. IU rem the case up and thread my die in til the die makes contact with the case. I turn the seater die up most of the way then I take a bullet and start seating it. I turn the seater die down untill I have the OAL that I want. Next I back off the seater stem at least two turns and I turn the die body into the press till I get the crimp I want and loct the die in place with the lock ring. Lastly I turn the seater rod back down so that it just makes contact with the bullet and I set thge lock nut.

I take my next case and charge it and lace a bullet over the case and set the case with bullet into my shell holder and lightly press the bullet home. I then remove the finished cartridge and check crimp and OAL and adjust if I have to.
 
Good post,Sir G

The finer points of crimping technique,such as trimming,are one issue.

But you address the very common error of running the seater die down to the shellholder.

And,yes! It sure does crush the cases ,causing the shoulder to expand.

Many folks have posted "Why do my reloads get stuck in the chamber of my AR with the bolt not quite closed"

That's why.
 
The rifle probably doesn't need the crimp,
But I get better consistancy in velocity with a medium heavy crimp.

Don't ask me why, it just seems to be that way.
The high/low velocity spread closes up,
While average velocity stays about the same.

Just a quirk? I don't know.
Don't know what others have seen, but this is my experience.
Click to expand...
The crimp will add a little pressure the load as it overcomes the crimp. It is said to make your load a cleaner more efficient burn. I noticed with my non-crimped 5.56 loads the cases are dirty. Crimped factory loads look a lot cleaner.
 
But you don't have the same bulk grade powder the factory loads with, so you are comparing apples to oranges until you see how it affects your own loads.

Nobody I am aware of who is loading match ammunition, including military match ammunition, uses a crimp. With ball ammo it probably helps pass the military low temperature ignition tests (-65°F), but matches aren't shot in those conditions. For match ammunition the distortion of the bullet is considered a more critical accuracy issue than start pressure. This is one reason match bullets don't have crimp cannelures. The other is that it is hard for manufacturers to put a crimp cannelure into a bullet's jacket without causing some degree of distortion.
 
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