neck turning & expander mandrel

[LC Tikka]

Hi all
When and why is the neck expander used.
Thinking of buying a K&M setup with .284 /7mm pilot for 284 win cases, won't the std pilot fit new cases?
Starting out with factory rounds, as no brass available in Australia, can I expect the std mandrel to properly fit once fired cases? The plan is to lightly turn for a .317" dia camber neck.
LC

 

[Laurie]

won't the std pilot fit new cases?

Maybe yes, more likely not. Moreover, new cases are often anything but true so they won't fit the turner mandrel easily or properly, or maybe even at all if there is a small flat in the circumference.

You really do need to use an expander mandrel, and it's important to get it from the same maker as the turner so they're closely matched. If you do a lot of turning in a particular calibre, or want really precise and consistent results, the more expensive carbide turner mandrels are definitely worth having - stay cooler with less friction.

If you don't expand the necks with a matched mandrel, the risks are too loose a fit on the turner with poor results - but this rarely happens. Much more common is too tight a fit, excess friction, the mandrel and case run hot and can even nearly seize up despite using adequate quantities of a good lubricant. If the mandrel gets really hot - and it will if it's even marginally too tight in the the case-neck - it expands and gets tighter still creating a vicious circle. In such circumstances, you never ever get a good result.

 

[ShootDots]

You use the expander mandrel to "Iron out / make perfectly round" necks, so you can turn the necks while they are in fact round! Some people use just their dies to make the necks round>>>if you try that they are not REALLY, REALLY round, like with a mandrel. Also you, ideally, should use a mandrel to neck UP a case. Let's say you are going to make a .284Win. from a 6.5 x 284 piece of brass. Ideally, it would be better to use a carbide mandrel (lube it) for that purpose over a stainless one. Carbide is considerably harder and more "lubricid" and will allow the expansion to take place easier. Then while it is expanded and nice and round, turn that neck down slightly past the neck shoulder junction, thus removing the "potential donut" before it goes to the inside of the case. Also, a little trick here: because it is virgin brass, there is alot of elasticity still in it and usually you can seat your bullets straight from the turning mandrel, as the "spring-back" will usually give you NOT ONLY PERFECTLY ROUND necks with ZERO runout, you will have almost exactly 1K neck tension. You will have to try your brass for that "trick' but I have not found any virgin brass and in many cases, freshly annealed brass, that wont grip a bullet with right at 1K neck tension from the mandrel...

As Laurie just stated, about the generation of heat surrounding the case / mandrel, I use a carbide mandrel for everything, sizing and turning and I have not YET experienced that level of heat generation.