Necking down 300 SAUM

[Ovenpaa]

Morning all!

I am preparing Norma 300 SAUM for my soon to be here 7mm, first stage for me is to neck down to chamber size followed by mandrel to true the neck diameter back before continuing with neck turn and final size.

This is throwing up some questions for me, the neck run out is all over the place after I have necked down both before and after I have run the mandrel through, I am used to a similar process with a 22-6.5X47 which would typically give a maximum of 5 thou run out at this stage but the 7mm is anywhere between 3 and 10 thou, it is far from finished but still seems excessive.

Also is there preferred sequence for preparing the brass and the neck turning?

[RAVEN]

Neck turn for close chamber fit fire form then run through neck turn mandrel and turn again this is the best way to get consistent neck walls
Cheers
RB

[Ovenpaa]

Neck turn for close chamber fit fire form then run through neck turn mandrel and turn again this is the best way to get consistent neck walls
Cheers
RB

Thanks for the reply. I assume I should neck it down from 300 to 7mm first, then neck turn?

[AlanF]

...I assume I should neck it down from 300 to 7mm first, then neck turn?

Ovenpaa,

Not sure which way Raven will recommend, but there is an important advantage in turning while still at 300 neck. If you turn all the way into the neck shoulder junction, then because the neck will shorten when you size down to 7mm, the turned part of the brass will actually sneak up the shoulder a little, which should mean you will never have a donut problem.

Alan

[Ovenpaa]

Now that is a handy tip!

So I need not worry about neck run out at these early stages and only expect decent readings after fire forming? (For neck run out I mean how much the neck is out of alignment to the case)

[AlanF]

You may get a few necks that are so badly aligned that they won't chamber, which you may have to discard. But if you can chamber them, even if they need a little force, then fire-forming will do wonders in straightening them - the worst ones may need a second firing to come good.

Alan

[RAVEN]

Necking down to 7mm then turning saves you a set of 30cal stuff
Turn into the shoulder a little and Alan you are right you will have no donut problems.
Any slight cut edge on the shoulder will be hammered by firing a few times to the inside below the neck.
Neck turning twice just makes them more uniform IMO
Cheers
RB

[RAVEN]

Some advice Alan gave me don't fire form them to hard use a mild load so it gives the primer pockets a chance to harden up your brass will last longer.
Cheers
RB