Guys,
When expanding necks to a larger size to establish a false shoulder for headspacing purposes, is there a minimum 'up-sizing'? Often its just said 'one calibre' larger, but that's kind of hard when your dealing with a 0.510" cartridge! I'm having a tapered expander made ... would 0.520" be large enough to open necks up and then size down to form the false shoulder? Doing a similiar thing with a 0.458" calibre, how much larger in that case?
Cheers...
Con

Hey Con, I'd say it depends on how large the Neck in the Chamber is cut. You would want the Expanded Case Neck to be just large enough that it will not slip into the Chamber Neck. Then as you P-FLR the Case you can achieve a Crush Fit or Zero Headspace.

No way to predict what size the Chamber Neck is without doing some measuring.
1. You can use a Cerosafe Cast of the Chamber.
2. Some l-o-n-g Pin Gauges from a machine shop or Quality Inspection Department.
3. If you had a Tapered "soft" rod you could slide it into the Chamber until it touches the beginning of the Chamber Neck, turn it just a bit to put a Witness Mark on the Rod and measure that.

If someone knows another way to do it, I'll learn something in this thread. Best of luck to you.

Hope I'm understanding the question right. I've used .416 Rem to form 375 Ackley, .375 H&H to form 338-8MM Mag., and 30-06 to do 280 Rem. All worked fine, size down to a slight crush fit and have at it. You need a fairly stiff load to insure complete forming. No belt on your case?

MTM,
That's right. Cartridge is the 458AR so no belt ... inadvertantly in haste screwed the die down too far and knocked the shoulders back to the point where misfires take place. So I'd like to expand the neck, bring it back down with the FL die and use the false shoulder to re-establish headspace. Fireformed some 300RUM opened, trimmed and without the shoulder pushed back yesterday and they all fired fine. So I'm just trying to recover the 50 pieces of brass I stuffed up. I suppose I coudl use a piece of cellophane tape wrapped around the base but behind the expansion point to tighten the case in the chamber ... that works too!

But ... we're also opening 416Rigby to 500AR ... that one will have very little shoulder to headspace on in its unformed state. I might just throw them up 0.015" and see how we go.

HotCore,
Woudlnt a fired case be a good approximation of the neck diameter? I coudl use that plus 0.015"??
Cheers...
Con

Hey Con, Using the Fired Case is better than nothing. It just depends on how far it Shrank-Back after the Expansion.

0.015" might do fine, or it may be more than needed - I don't know because I haven't got any first-hand experience Reloading a Cartridge that size. You can always try one and see what happens.

I would encourage you to consider Annealing them so you do not Work Harden the Necks. Cases that size have to be expensive and a bit of Annealing might save a few in the long run.

Maybe the guys on the Big Bore Board would have the first-hand knowledge that would help you.

I wish I could help you, but I just don't know. Best of luck with saving them.

I don't think it is possible to spit out minimum diameter increase that will work. You have figure out what will work. Bigger is better if it doesn't ruin your brass.
The angle of the case shoulder, how smooth your chamber is, how deep you seat your bullets and several other small variables can affect how the false shoulder works.

I've decided to try creating a false shoulder for a 300 win mag with new Nosler brass. The new brass measures 2.251" with the Hornady Head & Shoulders Gauge and I know this gun's shoulder will let brass expand to 2.2725" before I get a crush fit. So there is .0215" of initial expansion at the shoulder.

The closest caliber dies I have above the 300 win mag is for 338 win mag. Didn't take long to figure out that the Lee Collets do not work. So I dug around my bench drawers and found an RCBS FL die in 300 win mag and 338 win mag. The brass neck expanded with effort and lube to the 338 win mag FL die expander and then I set the 300 win mag FL die to size about 3/4 of the neck



I started neck sizing only with the 300 win mag die and adjusted it in until it would chamber but with a severe crush fit. That should keep the case from moving forward when the firing pin hits and lessen the initial thinning at the pressure ring and lessen the chance of a future case head separation.

Gonna load up five and shoot them to see how it works.

Con, when making 9.3 cases from 30-06 I usually take the neck (in stages) up to 416 to make that false shoulder, then neck back down to 9.3.
That gives me .020" per side to chamber on, which seems to be plenty.
Arguably, I could use a 375 expander to get the same effect, but the larger shoulder seems to minimise case loss due to excessive headspace.

In your case, maybe the 470 neck expander? then neck size as usual?

quote:

... bit of Annealing might save a few in the long run.

It might just save a lot of cases!

Refering to woods picture - I've done that!

quote:

Originally posted by 303Guy:

quote:

... bit of Annealing might save a few in the long run.

It might just save a lot of cases!

Refering to woods picture - I've done that!

Turtle neck brass...when you try to size it down too much in one pass or the brass is too soft.
I have lots of it in a scrap box.
I save cruddy and worn brass just for such testing.