Partial Neck Sizing

[fe1]

What is the purpose of partial neck sizing? Is it for shooting flat base bullets that don't go completely through the shoulder neck junction?

 

[357Mag]

Fe1 -

Howdy !

Not necessarily an answer, just some observations.....

Many traditional style necks-size dies and bushing-type NS dies, won't size the entire length of the neck.

I have a LEE " collet NS die" for .35 Rem, and I don't believe it sizes the entire length of the neck.

In many applications/chamber & leade set-ups, bullets are seated only partially down-into the case' necks.
And, there a whole lot of shooters who have had success when operating w/ only partially-sized necks.

With regards,
357Mag

 

[nonliberal]

The purpose is the unsized portion of the neck fits the chamber and is supposed to help center the cartridge in the chamber and keep the bullet more in line with the bore. I have not really seen any change in acuracy one way or the other, but I do it anyway just because it sounds reasonable and don't hurt since I use short bullets.

 

[gambleone]

Less brass to rework also.

 

[Shynloco]

What is the purpose of partial neck sizing? Is it for shooting flat base bullets that don't go completely through the shoulder neck junction?

IMHO, both comments ahead of mine apply. Some serious competitors recommend against it because the bullet pressure ring (the largest part of the bullet) is often sitting below the sized portion of the neck. They recommend that enough of the neck should be sized to hold the entire bullet inside the neck. That's not to say you must size the entire neck of the casing. But that can be controlled in how you set up your FL die )or have it custom made) when FL sizing. You can leave a small unsized portion to hold proper bullet alignment. Those recommendations are documented in Mike Ratigan's book, entitled, Extreme Rifle Accuracy. I shooting strictly for accuracy these days and have found no benefit in half neck sizing no matter the caliber and in fact use a Mandrel Die to size my necks for best concentricity and runout.

 

[Edo]

What is the purpose of partial neck sizing? Is it for shooting flat base bullets that don't go completely through the shoulder neck junction?

I shooting strictly for accuracy these days and have found no benefit in half neck sizing no matter the caliber and in fact use a Mandrel Die to size my necks for best concentricity and runout.

I'm curious how you get the necks small enough on fired cases to use the mandrel die. Do you use a FL or neck die and take out the expander plug?

 

[243winxb]

This >

The purpose is the unsized portion of the neck fits the chamber and is supposed to help center the cartridge in the chamber and keep the bullet more in line with the bore.

My testing with a Rem 40X single shot, factory chamber, shows sizing about 1/2 of the neck is more accurate than sizing more of the neck. Redding FL Type -S bushing die & controling shoulder bump. Bench Rest prepped brass. Doing your own testing is the only way to know.

 

[infantrytrophy]

This probably is not what you were looking for, but one use for partial neck sizing is to fireform brass for a wildcat caliber. You leave a little collar or "false shoulder" on which the case "headspaces" in the chamber. When fired, the shoulder is blown forward. This method is used to fireform 6 Dasher and 6 BRX from 6mmBR brass, and to form 6mmAR (and variants) and 6RAT from 6.5 Grendel brass. There are many others.

Example below - fireforming 6.5 Grendel to 6RAT:

Randy

 

[amlevin]

This >

The purpose is the unsized portion of the neck fits the chamber and is supposed to help center the cartridge in the chamber and keep the bullet more in line with the bore.

My testing with a Rem 40X single shot, factory chamber, shows sizing about 1/2 of the neck is more accurate than sizing more of the neck. Redding FL Type -S bushing die & controling shoulder bump. Bench Rest prepped brass. Doing your own testing is the only way to know.

Agree. I think any improvement of accuracy will depend on whether one has a custom chamber that does a great job of centering to begin with or a factory chamber that's somewhat loose.

 

[Shynloco]

Edo,
I use the FL Die with the expander ball removed as you said. The next step is the Mandrel Die which is why I have two presses side by side (Redding Big Boss with the Redding FL Die and the RCBS Rock Chucker having the Mandrel Die) so as not to slow the resizing process.