Necking by the head

[dalek]

I ran the following brass through some .357 carbide dies and saw a bit of a neck forming by the head:

What could cause that? User error? Die error? Error error?

[runfiverun]

that is where the size die stops sizing the case.

[dalek]

So I should not worry about it?

[GasGuzzler]

If they chamber easily I would not.

[runfiverun]

not a lot you can do about it either.
the ring in the carbide die is slightly tapered at the bottom but sizes the whole case down to one size.
if your getting a bunch of neck tension like 350 ID you can polish the ring out larger to work the brass less.
the extra .005 down is quite a bit when you figure the in and out each time you fire and size the round.

[Archer]

Brass is a consumable.
IF / When it loses neck tension or starts cracking toss it and start with fresh.
Sometimes that necking may be a bit excessive but others it may just be an optical effect of the sizing die polishing that portion of the brass that it sizes.
Don't fret it much it ain't that big a deal.

P.S.
I find quite often the expander die is more likely a culprit in overworking the brass.
I'm a big fan of the Lyman M dies to avoid that as they also tend to maintain alignment of the bullet with the case axis. A lot of other brands 'bell' the brass and allow the bullet to tip off axis. The M die is a two step so you can expand the case mouth AND control the belling from zero to more than you need.

[Missionary]

Good morning
My dies are generally set to only "neck size" my brass. The brass is segregated to certain firearms also.
Still shooting some of the original "100" 41 mag brass purchased in 1982. Granted those only receive plinking type hand loads.
Only time my brass gets full length resized is after near max loads that will not rechamber after firing.

NOE Molds is selling well made diameter specific neck expanders that are great for cast bullets.

[dalek]

Missionary, what I was told about dies was for bottle neck brass: neck size for bolt action and full size for semiauto. Straight wall stuff was/is/will be a mystery to me.

[runfiverun]

Mike [missionary] is talking about the revolver stuff same as I am.
controlling the sizing and the flair is one of the better way's to get good groups. [and to lengthen brass life]
both of us shoot cast bullets so learning to not squish them and to start them straight towards the barrel is something we have both learned leads to better accuracy.