Case forming - Neck up or Neck down ?

Pathfinder

Pathfinder

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Northeast Ontario
The only wildcat case forming ive down was a neck down from .284 to .264 and that went well. (7mm mauser to 6.5x257 Roberts)

Ive heard some say that necking up is bad because it weakens the case ?

Just wondering what the wisdom is on this, for a different gun I was going to neck up from 257 to 264 , which I though was fairly common. (25-06 to 6.5-06) .
 
It really depends on how much you stretch the neck. Usually it's a no issue thing. I neck a lot of .300 Win Mag to .358 without issues (in two passes).
 
I've been forming up and down a fair bit in the last two years.

8x57JS to 9.3x57 - one pass.
30-06 to 8x57 JS - one pass with decapping rod out and trim.
30-06 to 9.3x62 -one pass.
.270 to 30-06 (or the other way around) -one pass. .270 to 30-06 needs trimming.
30-06 to 6.5x55 - one pass with decapping rod out and then trim. Neck needs thinning.
30-06 to 25-06 - one pass on neck with 6.5x55 die and then one pass on 25-06 die. (straight 30-06 to 25-06, or even .270 to 25-06 gives me caved in necks 75% of the time). Neck needs thinning whether made from .270 or 30-06.
7mm rem mag to 338 win mag - one pass.

I have never had any real issues going smaller or larger to be honest. I'm not cheap with the lube however.
 
I necked up .243 brass to .260. It formed a "doughnut" after fireforming, a slightly thicker band on the inside at the base of the neck. That was easily removed though with a Forster inside neck trimmer.

The neck also comes out a little thicker, but that is Lapua brass and it is thicker to begin with.
 
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