Confused about 9mm

[bigfinger76]

Hey guys,
I'm not planning on loading for the 9mm, but I do have a question about it out of simple curiosity.
To my understanding, the 9mm has a tapered case. I load for .40 so I understand bearing surface/neck tension, which leads to my confusion. It seems to me that a tapered case would only allow for very minimal case tension. In other words, with a tapered case, the only portion of the case that could contact the bullet would be right at the case mouth. Any more would crimp the bullet, correct? So how is it possible to get sufficient neck tension?
Odd question, I know, but it's strange things like this that tend to bounce around in my head at night when I'm trying to go to sleep. So help me get some rest.

 

[rcmodel]

Weel?

When the factories do it, there is no noticeable bulge in the case at the base of the bullet.
They use factory magic carbide case forming dies only available to them.

When we reloaders do it?
Most sizing dies have a carbide sizing ring and do not taper size the case back to the factory taper.

They size the neck and body somewhere between too much, and just right.

So the part of the case the bullet is held by is not so tapered anymore.
And you probably can see the base of the bullet bulge in the case wall when you have proper case neck tension.

But that works just fine too.

rc

 

[B&C_C]

Yep - I concur with RC - I use to stay up at night worrying about "bulge" RC described :banghead:. Damned factory loaders, I never knew. And welcome to the sickness of reloading - got a Chrony yet ?

 

[bigfinger76]

Cool, thanks man. So I guess the fact that the 9 headspaces on the case mouth makes the perfect taper less important.

Like I said, I don't load 9mm (don't even own a 9mm). Just annoying curiosity! I'm used to slight bulge from loading .40, though.

One more thing...

What is "Weel"?

 

[rcmodel]

What is "Weel"?

Weel is supposed to be a long drawn out Kansas accent 'Well', like in pondering the question before answering for you city boys.

Never mind.

You had to be there to get it.

No harm, no foul!
O.K.?

So I guess the fact that the 9 headspaces on the case mouth makes the perfect taper less important.

About all auto pistol calibers headspace on the case mouth.
Most auto pistol calibers are straight wall cases.

So factory 9mm case taper actually has nothing to do with headspace at all.

When you get into bottleneck rifle calibers then the shoulder sets headspace in the chamber.
And the exact placement of the setback of the 'taper' of the shoulder makes all the difference in the world.

rc

 

[bigfinger76]

Thanks!

 

[1SOW]

A typical seating depth might be .2xx". After resizing the case, that will all be firm against the bullet. The taper crimp is adjustable to get it juuuuust right.---that's a Texan way of saying "precisely".